From 2001eeb5e6352996fd0d53a90b92629a56d7cb54 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 1 Jun 2020 19:29:22 -0700
Subject: [PATCH 01/29] value observer

---
 docs/examples/basic_meter/observer.py         |  3 +-
 .../ext/system_metrics/__init__.py            | 19 +++++++---
 opentelemetry-api/CHANGELOG.md                |  3 ++
 .../src/opentelemetry/metrics/__init__.py     | 20 +++++++++-
 opentelemetry-sdk/CHANGELOG.md                |  3 ++
 .../src/opentelemetry/sdk/metrics/__init__.py | 11 +++---
 .../sdk/metrics/export/aggregate.py           |  2 +-
 .../sdk/metrics/export/batcher.py             |  8 ++--
 .../tests/metrics/export/test_export.py       | 38 +++++++++----------
 .../tests/metrics/test_metrics.py             | 18 ++++-----
 10 files changed, 78 insertions(+), 47 deletions(-)

diff --git a/docs/examples/basic_meter/observer.py b/docs/examples/basic_meter/observer.py
index 0490fbe8efb..409402fa1cd 100644
--- a/docs/examples/basic_meter/observer.py
+++ b/docs/examples/basic_meter/observer.py
@@ -19,7 +19,7 @@
 import psutil
 
 from opentelemetry import metrics
-from opentelemetry.sdk.metrics import MeterProvider
+from opentelemetry.sdk.metrics import MeterProvider, ValueObserver
 from opentelemetry.sdk.metrics.export import ConsoleMetricsExporter
 from opentelemetry.sdk.metrics.export.batcher import UngroupedBatcher
 from opentelemetry.sdk.metrics.export.controller import PushController
@@ -45,6 +45,7 @@ def get_cpu_usage_callback(observer):
     description="per-cpu usage",
     unit="1",
     value_type=float,
+    observer_type=ValueObserver,
     label_keys=("cpu_number",),
 )
 
diff --git a/ext/opentelemetry-ext-system-metrics/src/opentelemetry/ext/system_metrics/__init__.py b/ext/opentelemetry-ext-system-metrics/src/opentelemetry/ext/system_metrics/__init__.py
index 88f36f4ac48..09c633f14b4 100644
--- a/ext/opentelemetry-ext-system-metrics/src/opentelemetry/ext/system_metrics/__init__.py
+++ b/ext/opentelemetry-ext-system-metrics/src/opentelemetry/ext/system_metrics/__init__.py
@@ -58,6 +58,7 @@
 import psutil
 
 from opentelemetry import metrics
+from opentelemetry.sdk.metrics import ValueObserver
 from opentelemetry.sdk.metrics.export import MetricsExporter
 from opentelemetry.sdk.metrics.export.controller import PushController
 
@@ -106,6 +107,7 @@ def __init__(
             description="System memory",
             unit="bytes",
             value_type=int,
+            observer_type=ValueObserver,
         )
 
         self.meter.register_observer(
@@ -114,6 +116,7 @@ def __init__(
             description="System CPU",
             unit="seconds",
             value_type=float,
+            observer_type=ValueObserver,
         )
 
         self.meter.register_observer(
@@ -122,6 +125,7 @@ def __init__(
             description="System network bytes",
             unit="bytes",
             value_type=int,
+            observer_type=ValueObserver,
         )
 
         self.meter.register_observer(
@@ -130,6 +134,7 @@ def __init__(
             description="Runtime memory",
             unit="bytes",
             value_type=int,
+            observer_type=ValueObserver,
         )
 
         self.meter.register_observer(
@@ -138,6 +143,7 @@ def __init__(
             description="Runtime CPU",
             unit="seconds",
             value_type=float,
+            observer_type=ValueObserver,
         )
 
         self.meter.register_observer(
@@ -146,9 +152,10 @@ def __init__(
             description="Runtime: gc objects",
             unit="objects",
             value_type=int,
+            observer_type=ValueObserver,
         )
 
-    def _get_system_memory(self, observer: metrics.Observer) -> None:
+    def _get_system_memory(self, observer: metrics.ValueObserver) -> None:
         """Observer callback for memory available
 
         Args:
@@ -161,7 +168,7 @@ def _get_system_memory(self, observer: metrics.Observer) -> None:
                 getattr(system_memory, metric), self._system_memory_labels
             )
 
-    def _get_system_cpu(self, observer: metrics.Observer) -> None:
+    def _get_system_cpu(self, observer: metrics.ValueObserver) -> None:
         """Observer callback for system cpu
 
         Args:
@@ -174,7 +181,7 @@ def _get_system_cpu(self, observer: metrics.Observer) -> None:
                 getattr(cpu_times, _type), self._system_cpu_labels
             )
 
-    def _get_network_bytes(self, observer: metrics.Observer) -> None:
+    def _get_network_bytes(self, observer: metrics.ValueObserver) -> None:
         """Observer callback for network bytes
 
         Args:
@@ -187,7 +194,7 @@ def _get_network_bytes(self, observer: metrics.Observer) -> None:
                 getattr(net_io, _type), self._network_bytes_labels
             )
 
-    def _get_runtime_memory(self, observer: metrics.Observer) -> None:
+    def _get_runtime_memory(self, observer: metrics.ValueObserver) -> None:
         """Observer callback for runtime memory
 
         Args:
@@ -200,7 +207,7 @@ def _get_runtime_memory(self, observer: metrics.Observer) -> None:
                 getattr(proc_memory, _type), self._runtime_memory_labels
             )
 
-    def _get_runtime_cpu(self, observer: metrics.Observer) -> None:
+    def _get_runtime_cpu(self, observer: metrics.ValueObserver) -> None:
         """Observer callback for runtime CPU
 
         Args:
@@ -213,7 +220,7 @@ def _get_runtime_cpu(self, observer: metrics.Observer) -> None:
                 getattr(proc_cpu, _type), self._runtime_cpu_labels
             )
 
-    def _get_runtime_gc_count(self, observer: metrics.Observer) -> None:
+    def _get_runtime_gc_count(self, observer: metrics.ValueObserver) -> None:
         """Observer callback for garbage collection
 
         Args:
diff --git a/opentelemetry-api/CHANGELOG.md b/opentelemetry-api/CHANGELOG.md
index 386bd75d470..dc9247305f9 100644
--- a/opentelemetry-api/CHANGELOG.md
+++ b/opentelemetry-api/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+- Rename Observer to ValueObserver
+  ([#751](https://github.com/open-telemetry/opentelemetry-python/pull/751))
+
 ## 0.8b0
 
 Released 2020-05-27
diff --git a/opentelemetry-api/src/opentelemetry/metrics/__init__.py b/opentelemetry-api/src/opentelemetry/metrics/__init__.py
index b7ad62adb2e..1fefed31061 100644
--- a/opentelemetry-api/src/opentelemetry/metrics/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/metrics/__init__.py
@@ -173,7 +173,6 @@ class Observer(abc.ABC):
     """An observer type metric instrument used to capture a current set of
     values.
 
-
     Observer instruments are asynchronous, a callback is invoked with the
     observer instrument as argument allowing the user to capture multiple
     values per collection interval.
@@ -201,6 +200,18 @@ def observe(self, value: ValueT, labels: Dict[str, str]) -> None:
         """
 
 
+class ValueObserver(Observer):
+    """No-op implementation of ``ValueObserver``."""
+
+    def observe(self, value: ValueT, labels: Dict[str, str]) -> None:
+        """Captures ``value`` to the valueobserver.
+
+        Args:
+            value: The value to capture to this valueobserver metric.
+            labels: Labels associated to ``value``.
+        """
+
+
 class MeterProvider(abc.ABC):
     @abc.abstractmethod
     def get_meter(
@@ -251,7 +262,10 @@ def get_meter(
         return DefaultMeter()
 
 
-MetricT = TypeVar("MetricT", Counter, Measure, Observer)
+MetricT = TypeVar("MetricT", Counter, Measure)
+InstrumentT = TypeVar("InstrumentT", Counter, Measure, Observer)
+# TODO: Will populate with other observers when implemented
+ObserverT = TypeVar("ObserverT", DefaultObserver, ValueObserver)
 ObserverCallbackT = Callable[[Observer], None]
 
 
@@ -302,6 +316,7 @@ def create_metric(
             unit: Unit of the metric values following the UCUM convention
                 (https://unitsofmeasure.org/ucum.html).
             value_type: The type of values being recorded by the metric.
+            observer_type: The type of observer being registered.
             metric_type: The type of metric being created.
             label_keys: The keys for the labels with dynamic values.
             enabled: Whether to report the metric by default.
@@ -316,6 +331,7 @@ def register_observer(
         description: str,
         unit: str,
         value_type: Type[ValueT],
+        observer_type: Type[ObserverT],
         label_keys: Sequence[str] = (),
         enabled: bool = True,
     ) -> "Observer":
diff --git a/opentelemetry-sdk/CHANGELOG.md b/opentelemetry-sdk/CHANGELOG.md
index 50ea751e15d..b4b8d3d4736 100644
--- a/opentelemetry-sdk/CHANGELOG.md
+++ b/opentelemetry-sdk/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+- Rename Observer to ValueObserver
+  ([#751](https://github.com/open-telemetry/opentelemetry-python/pull/751))
+
 ## 0.8b0
 
 Released 2020-05-27
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index 1d35648fd35..3bc05e3659c 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -190,8 +190,8 @@ def record(
     UPDATE_FUNCTION = record
 
 
-class Observer(metrics_api.Observer):
-    """See `opentelemetry.metrics.Observer`."""
+class ValueObserver(metrics_api.ValueObserver):
+    """See `opentelemetry.metrics.ValueObserver`."""
 
     def __init__(
         self,
@@ -257,7 +257,7 @@ class Record:
 
     def __init__(
         self,
-        metric: metrics_api.MetricT,
+        instrument: metrics_api.InstrumentT,
         labels: Dict[str, str],
         aggregator: Aggregator,
     ):
@@ -375,10 +375,11 @@ def register_observer(
         description: str,
         unit: str,
         value_type: Type[metrics_api.ValueT],
+        observer_type = Type[metrics_api.ObserverT],
         label_keys: Sequence[str] = (),
         enabled: bool = True,
-    ) -> metrics_api.Observer:
-        ob = Observer(
+    ) -> metrics_api.ObserverT:
+        ob = observer_type(
             callback,
             name,
             description,
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py
index ea8c40a7e72..d628f0f7147 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py
@@ -125,7 +125,7 @@ def merge(self, other):
             )
 
 
-class ObserverAggregator(Aggregator):
+class ValueObserverAggregator(Aggregator):
     """Same as MinMaxSumCount but also with last value."""
 
     _TYPE = namedtuple("minmaxsumcountlast", "min max sum count last")
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index 7b599f4c7da..9e1f40b0a80 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -15,13 +15,13 @@
 import abc
 from typing import Sequence, Type
 
-from opentelemetry.metrics import Counter, Measure, MetricT, Observer
+from opentelemetry.metrics import Counter, Measure, MetricT, ValueObserver
 from opentelemetry.sdk.metrics.export import MetricRecord
 from opentelemetry.sdk.metrics.export.aggregate import (
     Aggregator,
     CounterAggregator,
     MinMaxSumCountAggregator,
-    ObserverAggregator,
+    ValueObserverAggregator,
 )
 
 
@@ -51,8 +51,8 @@ def aggregator_for(self, metric_type: Type[MetricT]) -> Aggregator:
             return CounterAggregator()
         if issubclass(metric_type, Measure):
             return MinMaxSumCountAggregator()
-        if issubclass(metric_type, Observer):
-            return ObserverAggregator()
+        if issubclass(metric_type, ValueObserver):
+            return ValueObserverAggregator()
         # TODO: Add other aggregators
         return CounterAggregator()
 
diff --git a/opentelemetry-sdk/tests/metrics/export/test_export.py b/opentelemetry-sdk/tests/metrics/export/test_export.py
index c77a132459c..4e94b249e3f 100644
--- a/opentelemetry-sdk/tests/metrics/export/test_export.py
+++ b/opentelemetry-sdk/tests/metrics/export/test_export.py
@@ -26,7 +26,7 @@
 from opentelemetry.sdk.metrics.export.aggregate import (
     CounterAggregator,
     MinMaxSumCountAggregator,
-    ObserverAggregator,
+    ValueObserverAggregator,
 )
 from opentelemetry.sdk.metrics.export.batcher import UngroupedBatcher
 from opentelemetry.sdk.metrics.export.controller import PushController
@@ -432,11 +432,11 @@ def test_concurrent_update_and_checkpoint(self):
             self.assertEqual(checkpoint_total, fut.result())
 
 
-class TestObserverAggregator(unittest.TestCase):
+class TestValueObserverAggregator(unittest.TestCase):
     @mock.patch("opentelemetry.sdk.metrics.export.aggregate.time_ns")
     def test_update(self, time_mock):
         time_mock.return_value = 123
-        observer = ObserverAggregator()
+        observer = ValueObserverAggregator()
         # test current values without any update
         self.assertEqual(observer.mmsc.current, (None, None, None, 0))
         self.assertIsNone(observer.current)
@@ -455,7 +455,7 @@ def test_update(self, time_mock):
         self.assertEqual(observer.current, values[-1])
 
     def test_checkpoint(self):
-        observer = ObserverAggregator()
+        observer = ValueObserverAggregator()
 
         # take checkpoint wihtout any update
         observer.take_checkpoint()
@@ -473,15 +473,15 @@ def test_checkpoint(self):
         )
 
     def test_merge(self):
-        observer1 = ObserverAggregator()
-        observer2 = ObserverAggregator()
+        observer1 = ValueObserverAggregator()
+        observer2 = ValueObserverAggregator()
 
         mmsc_checkpoint1 = MinMaxSumCountAggregator._TYPE(3, 150, 101, 3)
         mmsc_checkpoint2 = MinMaxSumCountAggregator._TYPE(1, 33, 44, 2)
 
-        checkpoint1 = ObserverAggregator._TYPE(*(mmsc_checkpoint1 + (23,)))
+        checkpoint1 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint1 + (23,)))
 
-        checkpoint2 = ObserverAggregator._TYPE(*(mmsc_checkpoint2 + (27,)))
+        checkpoint2 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint2 + (27,)))
 
         observer1.mmsc.checkpoint = mmsc_checkpoint1
         observer2.mmsc.checkpoint = mmsc_checkpoint2
@@ -507,15 +507,15 @@ def test_merge(self):
         self.assertEqual(observer1.last_update_timestamp, 123)
 
     def test_merge_last_updated(self):
-        observer1 = ObserverAggregator()
-        observer2 = ObserverAggregator()
+        observer1 = ValueObserverAggregator()
+        observer2 = ValueObserverAggregator()
 
         mmsc_checkpoint1 = MinMaxSumCountAggregator._TYPE(3, 150, 101, 3)
         mmsc_checkpoint2 = MinMaxSumCountAggregator._TYPE(1, 33, 44, 2)
 
-        checkpoint1 = ObserverAggregator._TYPE(*(mmsc_checkpoint1 + (23,)))
+        checkpoint1 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint1 + (23,)))
 
-        checkpoint2 = ObserverAggregator._TYPE(*(mmsc_checkpoint2 + (27,)))
+        checkpoint2 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint2 + (27,)))
 
         observer1.mmsc.checkpoint = mmsc_checkpoint1
         observer2.mmsc.checkpoint = mmsc_checkpoint2
@@ -541,15 +541,15 @@ def test_merge_last_updated(self):
         self.assertEqual(observer1.last_update_timestamp, 123)
 
     def test_merge_last_updated_none(self):
-        observer1 = ObserverAggregator()
-        observer2 = ObserverAggregator()
+        observer1 = ValueObserverAggregator()
+        observer2 = ValueObserverAggregator()
 
         mmsc_checkpoint1 = MinMaxSumCountAggregator._TYPE(3, 150, 101, 3)
         mmsc_checkpoint2 = MinMaxSumCountAggregator._TYPE(1, 33, 44, 2)
 
-        checkpoint1 = ObserverAggregator._TYPE(*(mmsc_checkpoint1 + (23,)))
+        checkpoint1 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint1 + (23,)))
 
-        checkpoint2 = ObserverAggregator._TYPE(*(mmsc_checkpoint2 + (27,)))
+        checkpoint2 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint2 + (27,)))
 
         observer1.mmsc.checkpoint = mmsc_checkpoint1
         observer2.mmsc.checkpoint = mmsc_checkpoint2
@@ -575,11 +575,11 @@ def test_merge_last_updated_none(self):
         self.assertEqual(observer1.last_update_timestamp, 100)
 
     def test_merge_with_empty(self):
-        observer1 = ObserverAggregator()
-        observer2 = ObserverAggregator()
+        observer1 = ValueObserverAggregator()
+        observer2 = ValueObserverAggregator()
 
         mmsc_checkpoint1 = MinMaxSumCountAggregator._TYPE(3, 150, 101, 3)
-        checkpoint1 = ObserverAggregator._TYPE(*(mmsc_checkpoint1 + (23,)))
+        checkpoint1 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint1 + (23,)))
 
         observer1.mmsc.checkpoint = mmsc_checkpoint1
         observer1.checkpoint = checkpoint1
diff --git a/opentelemetry-sdk/tests/metrics/test_metrics.py b/opentelemetry-sdk/tests/metrics/test_metrics.py
index 32980647055..35540ac57f8 100644
--- a/opentelemetry-sdk/tests/metrics/test_metrics.py
+++ b/opentelemetry-sdk/tests/metrics/test_metrics.py
@@ -83,7 +83,7 @@ def callback(observer):
             self.assertIsInstance(observer, metrics_api.Observer)
             observer.observe(45, {})
 
-        observer = metrics.Observer(
+        observer = metrics.ValueObserver(
             callback, "name", "desc", "unit", int, meter, (), True
         )
 
@@ -160,7 +160,7 @@ def test_register_observer(self):
         callback = mock.Mock()
 
         observer = meter.register_observer(
-            callback, "name", "desc", "unit", int, (), True
+            callback, "name", "desc", "unit", int, metrics.ValueObserver
         )
 
         self.assertIsInstance(observer, metrics_api.Observer)
@@ -180,7 +180,7 @@ def test_unregister_observer(self):
         callback = mock.Mock()
 
         observer = meter.register_observer(
-            callback, "name", "desc", "unit", int, (), True
+            callback, "name", "desc", "unit", int, metrics.ValueObserver
         )
 
         meter.unregister_observer(observer)
@@ -283,10 +283,10 @@ def test_record(self):
         )
 
 
-class TestObserver(unittest.TestCase):
+class TestValueObserver(unittest.TestCase):
     def test_observe(self):
         meter = metrics.MeterProvider().get_meter(__name__)
-        observer = metrics.Observer(
+        observer = metrics.ValueObserver(
             None, "name", "desc", "unit", int, meter, ("key",), True
         )
         labels = {"key": "value"}
@@ -303,7 +303,7 @@ def test_observe(self):
 
     def test_observe_disabled(self):
         meter = metrics.MeterProvider().get_meter(__name__)
-        observer = metrics.Observer(
+        observer = metrics.ValueObserver(
             None, "name", "desc", "unit", int, meter, ("key",), False
         )
         labels = {"key": "value"}
@@ -313,7 +313,7 @@ def test_observe_disabled(self):
     @mock.patch("opentelemetry.sdk.metrics.logger")
     def test_observe_incorrect_type(self, logger_mock):
         meter = metrics.MeterProvider().get_meter(__name__)
-        observer = metrics.Observer(
+        observer = metrics.ValueObserver(
             None, "name", "desc", "unit", int, meter, ("key",), True
         )
         labels = {"key": "value"}
@@ -325,7 +325,7 @@ def test_run(self):
         meter = metrics.MeterProvider().get_meter(__name__)
 
         callback = mock.Mock()
-        observer = metrics.Observer(
+        observer = metrics.ValueObserver(
             callback, "name", "desc", "unit", int, meter, (), True
         )
 
@@ -339,7 +339,7 @@ def test_run_exception(self, logger_mock):
         callback = mock.Mock()
         callback.side_effect = Exception("We have a problem!")
 
-        observer = metrics.Observer(
+        observer = metrics.ValueObserver(
             callback, "name", "desc", "unit", int, meter, (), True
         )
 

From 429339817cb71c2cfef9a72e6bcc1c02753e430a Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 1 Jun 2020 22:17:43 -0700
Subject: [PATCH 02/29] lint

---
 .../src/opentelemetry/sdk/metrics/__init__.py |  4 +--
 .../tests/metrics/export/test_export.py       | 28 ++++++++++++++-----
 2 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index 3bc05e3659c..8d36be3949e 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -261,7 +261,7 @@ def __init__(
         labels: Dict[str, str],
         aggregator: Aggregator,
     ):
-        self.metric = metric
+        self.instrument = instrument
         self.labels = labels
         self.aggregator = aggregator
 
@@ -375,7 +375,7 @@ def register_observer(
         description: str,
         unit: str,
         value_type: Type[metrics_api.ValueT],
-        observer_type = Type[metrics_api.ObserverT],
+        observer_type=Type[metrics_api.ObserverT],
         label_keys: Sequence[str] = (),
         enabled: bool = True,
     ) -> metrics_api.ObserverT:
diff --git a/opentelemetry-sdk/tests/metrics/export/test_export.py b/opentelemetry-sdk/tests/metrics/export/test_export.py
index 4e94b249e3f..5b8c2230bd8 100644
--- a/opentelemetry-sdk/tests/metrics/export/test_export.py
+++ b/opentelemetry-sdk/tests/metrics/export/test_export.py
@@ -479,9 +479,13 @@ def test_merge(self):
         mmsc_checkpoint1 = MinMaxSumCountAggregator._TYPE(3, 150, 101, 3)
         mmsc_checkpoint2 = MinMaxSumCountAggregator._TYPE(1, 33, 44, 2)
 
-        checkpoint1 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint1 + (23,)))
+        checkpoint1 = ValueObserverAggregator._TYPE(
+            *(mmsc_checkpoint1 + (23,))
+        )
 
-        checkpoint2 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint2 + (27,)))
+        checkpoint2 = ValueObserverAggregator._TYPE(
+            *(mmsc_checkpoint2 + (27,))
+        )
 
         observer1.mmsc.checkpoint = mmsc_checkpoint1
         observer2.mmsc.checkpoint = mmsc_checkpoint2
@@ -513,9 +517,13 @@ def test_merge_last_updated(self):
         mmsc_checkpoint1 = MinMaxSumCountAggregator._TYPE(3, 150, 101, 3)
         mmsc_checkpoint2 = MinMaxSumCountAggregator._TYPE(1, 33, 44, 2)
 
-        checkpoint1 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint1 + (23,)))
+        checkpoint1 = ValueObserverAggregator._TYPE(
+            *(mmsc_checkpoint1 + (23,))
+        )
 
-        checkpoint2 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint2 + (27,)))
+        checkpoint2 = ValueObserverAggregator._TYPE(
+            *(mmsc_checkpoint2 + (27,))
+        )
 
         observer1.mmsc.checkpoint = mmsc_checkpoint1
         observer2.mmsc.checkpoint = mmsc_checkpoint2
@@ -547,9 +555,13 @@ def test_merge_last_updated_none(self):
         mmsc_checkpoint1 = MinMaxSumCountAggregator._TYPE(3, 150, 101, 3)
         mmsc_checkpoint2 = MinMaxSumCountAggregator._TYPE(1, 33, 44, 2)
 
-        checkpoint1 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint1 + (23,)))
+        checkpoint1 = ValueObserverAggregator._TYPE(
+            *(mmsc_checkpoint1 + (23,))
+        )
 
-        checkpoint2 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint2 + (27,)))
+        checkpoint2 = ValueObserverAggregator._TYPE(
+            *(mmsc_checkpoint2 + (27,))
+        )
 
         observer1.mmsc.checkpoint = mmsc_checkpoint1
         observer2.mmsc.checkpoint = mmsc_checkpoint2
@@ -579,7 +591,9 @@ def test_merge_with_empty(self):
         observer2 = ValueObserverAggregator()
 
         mmsc_checkpoint1 = MinMaxSumCountAggregator._TYPE(3, 150, 101, 3)
-        checkpoint1 = ValueObserverAggregator._TYPE(*(mmsc_checkpoint1 + (23,)))
+        checkpoint1 = ValueObserverAggregator._TYPE(
+            *(mmsc_checkpoint1 + (23,))
+        )
 
         observer1.mmsc.checkpoint = mmsc_checkpoint1
         observer1.checkpoint = checkpoint1

From e65de5c30c25dab249bf9d098a568ade8bd8b646 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 1 Jun 2020 22:33:03 -0700
Subject: [PATCH 03/29] instrument

---
 opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py | 2 +-
 .../src/opentelemetry/sdk/metrics/export/__init__.py        | 2 +-
 .../src/opentelemetry/sdk/metrics/export/batcher.py         | 6 +++---
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index 8d36be3949e..734aeb27592 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -393,7 +393,7 @@ def register_observer(
             self.observers.add(ob)
         return ob
 
-    def unregister_observer(self, observer: "Observer") -> None:
+    def unregister_observer(self, observer: metrics_api.ObserverT) -> None:
         with self.observers_lock:
             self.observers.remove(observer)
 
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/__init__.py
index f5a8693268e..cc74df63c74 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/__init__.py
@@ -79,7 +79,7 @@ def export(
             print(
                 '{}(data="{}", labels="{}", value={})'.format(
                     type(self).__name__,
-                    record.metric,
+                    record.instrument,
                     record.labels,
                     record.aggregator.checkpoint,
                 )
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index 9e1f40b0a80..c03d72db31a 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -63,8 +63,8 @@ def checkpoint_set(self) -> Sequence[MetricRecord]:
         data in all of the aggregators in this batcher.
         """
         metric_records = []
-        for (metric, labels), aggregator in self._batch_map.items():
-            metric_records.append(MetricRecord(aggregator, labels, metric))
+        for (instrument, labels), aggregator in self._batch_map.items():
+            metric_records.append(MetricRecord(aggregator, labels, instrument))
         return metric_records
 
     def finished_collection(self):
@@ -90,7 +90,7 @@ class UngroupedBatcher(Batcher):
     def process(self, record):
         # Checkpoints the current aggregator value to be collected for export
         record.aggregator.take_checkpoint()
-        batch_key = (record.metric, record.labels)
+        batch_key = (record.instrument, record.labels)
         batch_value = self._batch_map.get(batch_key)
         aggregator = record.aggregator
         if batch_value:

From 38504d40f9bb2c7febe6ab7583982f416b14cbdc Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 2 Jun 2020 00:19:13 -0700
Subject: [PATCH 04/29] instrument

---
 .../src/opentelemetry/sdk/metrics/export/batcher.py             | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index c03d72db31a..f9c837a5687 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -101,6 +101,6 @@ def process(self, record):
         if self.stateful:
             # if stateful batcher, create a copy of the aggregator and update
             # it with the current checkpointed value for long-term storage
-            aggregator = self.aggregator_for(record.metric.__class__)
+            aggregator = self.aggregator_for(record.instrument.__class__)
             aggregator.merge(record.aggregator)
         self._batch_map[batch_key] = aggregator

From efd685e09cf9e7a4770279337a7427b4f38bc93c Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 2 Jun 2020 00:38:02 -0700
Subject: [PATCH 05/29] batcher

---
 .../src/opentelemetry/sdk/metrics/export/batcher.py    | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index f9c837a5687..ad79006acb5 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -41,17 +41,17 @@ def __init__(self, stateful: bool):
         # (deltas)
         self.stateful = stateful
 
-    def aggregator_for(self, metric_type: Type[MetricT]) -> Aggregator:
-        """Returns an aggregator based on metric type.
+    def aggregator_for(self, instrument_type: Type[InstrumentT]) -> Aggregator:
+        """Returns an aggregator based on metric instrument type.
 
         Aggregators keep track of and updates values when metrics get updated.
         """
         # pylint:disable=R0201
-        if issubclass(metric_type, Counter):
+        if issubclass(instrument_type, Counter):
             return CounterAggregator()
-        if issubclass(metric_type, Measure):
+        if issubclass(instrument_type, Measure):
             return MinMaxSumCountAggregator()
-        if issubclass(metric_type, ValueObserver):
+        if issubclass(instrument_type, ValueObserver):
             return ValueObserverAggregator()
         # TODO: Add other aggregators
         return CounterAggregator()

From e72f06a1f88756531fdf795a661dc981fca4b0ad Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 2 Jun 2020 00:51:14 -0700
Subject: [PATCH 06/29] InstrumentT

---
 .../src/opentelemetry/sdk/metrics/export/batcher.py             | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index ad79006acb5..b3ea4335068 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -15,7 +15,7 @@
 import abc
 from typing import Sequence, Type
 
-from opentelemetry.metrics import Counter, Measure, MetricT, ValueObserver
+from opentelemetry.metrics import Counter, Measure, InstrumentT, ValueObserver
 from opentelemetry.sdk.metrics.export import MetricRecord
 from opentelemetry.sdk.metrics.export.aggregate import (
     Aggregator,

From d0505d18f39f4be15c46abda2b47057e2ba0ea86 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 2 Jun 2020 01:07:34 -0700
Subject: [PATCH 07/29] mypy

---
 opentelemetry-api/src/opentelemetry/metrics/__init__.py         | 1 +
 .../src/opentelemetry/sdk/metrics/export/batcher.py             | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/opentelemetry-api/src/opentelemetry/metrics/__init__.py b/opentelemetry-api/src/opentelemetry/metrics/__init__.py
index 1fefed31061..21f245e0eeb 100644
--- a/opentelemetry-api/src/opentelemetry/metrics/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/metrics/__init__.py
@@ -389,6 +389,7 @@ def register_observer(
         description: str,
         unit: str,
         value_type: Type[ValueT],
+        observer_type: Type[ObserverT],
         label_keys: Sequence[str] = (),
         enabled: bool = True,
     ) -> "Observer":
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index b3ea4335068..977a8c72655 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -15,7 +15,7 @@
 import abc
 from typing import Sequence, Type
 
-from opentelemetry.metrics import Counter, Measure, InstrumentT, ValueObserver
+from opentelemetry.metrics import Counter, InstrumentT, Measure, ValueObserver
 from opentelemetry.sdk.metrics.export import MetricRecord
 from opentelemetry.sdk.metrics.export.aggregate import (
     Aggregator,

From f2e446237f96520f30f6ef53ff24e65b2d4dc9f8 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 2 Jun 2020 01:29:41 -0700
Subject: [PATCH 08/29] reorder metricrecord

---
 .../tests/test_otcollector_metrics_exporter.py         | 10 +++++-----
 .../tests/test_prometheus_exporter.py                  |  6 +++---
 .../src/opentelemetry/sdk/metrics/export/__init__.py   |  8 ++++----
 .../src/opentelemetry/sdk/metrics/export/batcher.py    |  2 +-
 opentelemetry-sdk/tests/metrics/export/test_export.py  |  2 +-
 5 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/ext/opentelemetry-ext-opencensusexporter/tests/test_otcollector_metrics_exporter.py b/ext/opentelemetry-ext-opencensusexporter/tests/test_otcollector_metrics_exporter.py
index 63ea28cd935..ca904fe7376 100644
--- a/ext/opentelemetry-ext-opencensusexporter/tests/test_otcollector_metrics_exporter.py
+++ b/ext/opentelemetry-ext-opencensusexporter/tests/test_otcollector_metrics_exporter.py
@@ -92,7 +92,7 @@ def test_get_collector_point(self):
             "testName", "testDescription", "unit", float, Measure
         )
         result = metrics_exporter.get_collector_point(
-            MetricRecord(aggregator, self._key_labels, int_counter)
+            MetricRecord(int_counter, self._key_labels, aggregator)
         )
         self.assertIsInstance(result, metrics_pb2.Point)
         self.assertIsInstance(result.timestamp, Timestamp)
@@ -100,13 +100,13 @@ def test_get_collector_point(self):
         aggregator.update(123.5)
         aggregator.take_checkpoint()
         result = metrics_exporter.get_collector_point(
-            MetricRecord(aggregator, self._key_labels, float_counter)
+            MetricRecord(float_counter, self._key_labels, aggregator)
         )
         self.assertEqual(result.double_value, 123.5)
         self.assertRaises(
             TypeError,
             metrics_exporter.get_collector_point(
-                MetricRecord(aggregator, self._key_labels, measure)
+                MetricRecord(measure, self._key_labels, aggregator)
             ),
         )
 
@@ -122,7 +122,7 @@ def test_export(self):
             "testname", "testdesc", "unit", int, Counter, ["environment"]
         )
         record = MetricRecord(
-            aggregate.CounterAggregator(), self._key_labels, test_metric
+            test_metric, self._key_labels, aggregate.CounterAggregator(),
         )
 
         result = collector_exporter.export([record])
@@ -147,7 +147,7 @@ def test_translate_to_collector(self):
         aggregator = aggregate.CounterAggregator()
         aggregator.update(123)
         aggregator.take_checkpoint()
-        record = MetricRecord(aggregator, self._key_labels, test_metric)
+        record = MetricRecord(test_metric, self._key_labels, aggregator,)
         output_metrics = metrics_exporter.translate_to_collector([record])
         self.assertEqual(len(output_metrics), 1)
         self.assertIsInstance(output_metrics[0], metrics_pb2.Metric)
diff --git a/ext/opentelemetry-ext-prometheus/tests/test_prometheus_exporter.py b/ext/opentelemetry-ext-prometheus/tests/test_prometheus_exporter.py
index f986e0c4f5f..e97f8f4b459 100644
--- a/ext/opentelemetry-ext-prometheus/tests/test_prometheus_exporter.py
+++ b/ext/opentelemetry-ext-prometheus/tests/test_prometheus_exporter.py
@@ -67,7 +67,7 @@ def test_shutdown(self):
     def test_export(self):
         with self._registry_register_patch:
             record = MetricRecord(
-                CounterAggregator(), self._labels_key, self._test_metric
+                self._test_metric, self._labels_key, CounterAggregator(),
             )
             exporter = PrometheusMetricsExporter()
             result = exporter.export([record])
@@ -90,7 +90,7 @@ def test_counter_to_prometheus(self):
         aggregator = CounterAggregator()
         aggregator.update(123)
         aggregator.take_checkpoint()
-        record = MetricRecord(aggregator, key_labels, metric)
+        record = MetricRecord(metric, key_labels, aggregator, key_labels)
         collector = CustomCollector("testprefix")
         collector.add_metrics_data([record])
 
@@ -118,7 +118,7 @@ def test_invalid_metric(self):
         )
         labels = {"environment": "staging"}
         key_labels = metrics.get_labels_as_key(labels)
-        record = MetricRecord(None, key_labels, metric)
+        record = MetricRecord(metric, key_labels, None)
         collector = CustomCollector("testprefix")
         collector.add_metrics_data([record])
         collector.collect()
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/__init__.py
index cc74df63c74..16911f94efb 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/__init__.py
@@ -27,13 +27,13 @@ class MetricsExportResult(Enum):
 class MetricRecord:
     def __init__(
         self,
-        aggregator: Aggregator,
+        instrument: metrics_api.InstrumentT,
         labels: Tuple[Tuple[str, str]],
-        metric: metrics_api.MetricT,
+        aggregator: Aggregator,
     ):
-        self.aggregator = aggregator
+        self.instrument = instrument
         self.labels = labels
-        self.metric = metric
+        self.aggregator = aggregator
 
 
 class MetricsExporter:
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index 977a8c72655..d48fdbfeff6 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -64,7 +64,7 @@ def checkpoint_set(self) -> Sequence[MetricRecord]:
         """
         metric_records = []
         for (instrument, labels), aggregator in self._batch_map.items():
-            metric_records.append(MetricRecord(aggregator, labels, instrument))
+            metric_records.append(MetricRecord(instrument, labels, aggregator))
         return metric_records
 
     def finished_collection(self):
diff --git a/opentelemetry-sdk/tests/metrics/export/test_export.py b/opentelemetry-sdk/tests/metrics/export/test_export.py
index 5b8c2230bd8..af63fdff10e 100644
--- a/opentelemetry-sdk/tests/metrics/export/test_export.py
+++ b/opentelemetry-sdk/tests/metrics/export/test_export.py
@@ -48,7 +48,7 @@ def test_export(self):
         )
         labels = {"environment": "staging"}
         aggregator = CounterAggregator()
-        record = MetricRecord(aggregator, labels, metric)
+        record = MetricRecord(metric, labels, aggregator)
         result = '{}(data="{}", labels="{}", value={})'.format(
             ConsoleMetricsExporter.__name__,
             metric,

From 0d26ec6c119fe0fb89d043ae181aacc682878b94 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 2 Jun 2020 11:02:47 -0700
Subject: [PATCH 09/29] fix tests

---
 .../tests/test_prometheus_exporter.py                           | 2 +-
 .../tests/test_system_metrics.py                                | 2 +-
 opentelemetry-sdk/tests/metrics/export/test_export.py           | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/ext/opentelemetry-ext-prometheus/tests/test_prometheus_exporter.py b/ext/opentelemetry-ext-prometheus/tests/test_prometheus_exporter.py
index e97f8f4b459..1862f789c0c 100644
--- a/ext/opentelemetry-ext-prometheus/tests/test_prometheus_exporter.py
+++ b/ext/opentelemetry-ext-prometheus/tests/test_prometheus_exporter.py
@@ -90,7 +90,7 @@ def test_counter_to_prometheus(self):
         aggregator = CounterAggregator()
         aggregator.update(123)
         aggregator.take_checkpoint()
-        record = MetricRecord(metric, key_labels, aggregator, key_labels)
+        record = MetricRecord(metric, key_labels, aggregator)
         collector = CustomCollector("testprefix")
         collector.add_metrics_data([record])
 
diff --git a/ext/opentelemetry-ext-system-metrics/tests/test_system_metrics.py b/ext/opentelemetry-ext-system-metrics/tests/test_system_metrics.py
index 70ead2c5152..b2d6bab4015 100644
--- a/ext/opentelemetry-ext-system-metrics/tests/test_system_metrics.py
+++ b/ext/opentelemetry-ext-system-metrics/tests/test_system_metrics.py
@@ -54,7 +54,7 @@ def _assert_metrics(self, observer_name, system_metrics, expected):
         ):
             if (
                 metric.labels in expected
-                and metric.metric.name == observer_name
+                and metric.instrument.name == observer_name
             ):
                 self.assertEqual(
                     metric.aggregator.checkpoint.last, expected[metric.labels],
diff --git a/opentelemetry-sdk/tests/metrics/export/test_export.py b/opentelemetry-sdk/tests/metrics/export/test_export.py
index af63fdff10e..178e41b2134 100644
--- a/opentelemetry-sdk/tests/metrics/export/test_export.py
+++ b/opentelemetry-sdk/tests/metrics/export/test_export.py
@@ -90,7 +90,7 @@ def test_checkpoint_set(self):
         batcher._batch_map = _batch_map
         records = batcher.checkpoint_set()
         self.assertEqual(len(records), 1)
-        self.assertEqual(records[0].metric, metric)
+        self.assertEqual(records[0].instrument, metric)
         self.assertEqual(records[0].labels, labels)
         self.assertEqual(records[0].aggregator, aggregator)
 

From 68f980efb0824d45cf073e1670daaee761962bc3 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 2 Jun 2020 11:25:59 -0700
Subject: [PATCH 10/29] fix tests

---
 .../metrics_exporter/__init__.py                   | 14 +++++++-------
 .../src/opentelemetry/ext/prometheus/__init__.py   | 12 ++++++------
 .../opentelemetry/sdk/metrics/export/batcher.py    |  7 ++++++-
 3 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/ext/opentelemetry-ext-opencensusexporter/src/opentelemetry/ext/opencensusexporter/metrics_exporter/__init__.py b/ext/opentelemetry-ext-opencensusexporter/src/opentelemetry/ext/opencensusexporter/metrics_exporter/__init__.py
index faa0788c7f1..bb1a1ee888c 100644
--- a/ext/opentelemetry-ext-opencensusexporter/src/opentelemetry/ext/opencensusexporter/metrics_exporter/__init__.py
+++ b/ext/opentelemetry-ext-opencensusexporter/src/opentelemetry/ext/opencensusexporter/metrics_exporter/__init__.py
@@ -114,10 +114,10 @@ def translate_to_collector(
             )
 
         metric_descriptor = metrics_pb2.MetricDescriptor(
-            name=metric_record.metric.name,
-            description=metric_record.metric.description,
-            unit=metric_record.metric.unit,
-            type=get_collector_metric_type(metric_record.metric),
+            name=metric_record.instrument.name,
+            description=metric_record.instrument.description,
+            unit=metric_record.instrument.unit,
+            type=get_collector_metric_type(metric_record.instrument),
             label_keys=label_keys,
         )
 
@@ -151,14 +151,14 @@ def get_collector_point(metric_record: MetricRecord) -> metrics_pb2.Point:
             metric_record.aggregator.last_update_timestamp
         )
     )
-    if metric_record.metric.value_type == int:
+    if metric_record.instrument.value_type == int:
         point.int64_value = metric_record.aggregator.checkpoint
-    elif metric_record.metric.value_type == float:
+    elif metric_record.instrument.value_type == float:
         point.double_value = metric_record.aggregator.checkpoint
     else:
         raise TypeError(
             "Unsupported metric type: {}".format(
-                metric_record.metric.value_type
+                metric_record.instrument.value_type
             )
         )
     return point
diff --git a/ext/opentelemetry-ext-prometheus/src/opentelemetry/ext/prometheus/__init__.py b/ext/opentelemetry-ext-prometheus/src/opentelemetry/ext/prometheus/__init__.py
index cc44621ac48..59ef3f1708a 100644
--- a/ext/opentelemetry-ext-prometheus/src/opentelemetry/ext/prometheus/__init__.py
+++ b/ext/opentelemetry-ext-prometheus/src/opentelemetry/ext/prometheus/__init__.py
@@ -152,22 +152,22 @@ def _translate_to_prometheus(self, metric_record: MetricRecord):
         metric_name = ""
         if self._prefix != "":
             metric_name = self._prefix + "_"
-        metric_name += self._sanitize(metric_record.metric.name)
+        metric_name += self._sanitize(metric_record.instrument.name)
 
-        if isinstance(metric_record.metric, Counter):
+        if isinstance(metric_record.instrument, Counter):
             prometheus_metric = CounterMetricFamily(
                 name=metric_name,
-                documentation=metric_record.metric.description,
+                documentation=metric_record.instrument.description,
                 labels=label_keys,
             )
             prometheus_metric.add_metric(
                 labels=label_values, value=metric_record.aggregator.checkpoint
             )
         # TODO: Add support for histograms when supported in OT
-        elif isinstance(metric_record.metric, ValueRecorder):
+        elif isinstance(metric_record.instrument, ValueRecorder):
             prometheus_metric = UnknownMetricFamily(
                 name=metric_name,
-                documentation=metric_record.metric.description,
+                documentation=metric_record.instrument.description,
                 labels=label_keys,
             )
             prometheus_metric.add_metric(
@@ -176,7 +176,7 @@ def _translate_to_prometheus(self, metric_record: MetricRecord):
 
         else:
             logger.warning(
-                "Unsupported metric type. %s", type(metric_record.metric)
+                "Unsupported metric type. %s", type(metric_record.instrument)
             )
         return prometheus_metric
 
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index c1c549b9a15..f5158e1a247 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -15,7 +15,12 @@
 import abc
 from typing import Sequence, Type
 
-from opentelemetry.metrics import Counter, InstrumentT, ValueRecorder, ValueObserver
+from opentelemetry.metrics import (
+    Counter,
+    InstrumentT,
+    ValueRecorder,
+    ValueObserver,
+)
 from opentelemetry.sdk.metrics.export import MetricRecord
 from opentelemetry.sdk.metrics.export.aggregate import (
     Aggregator,

From bf17d2d0d6a5b540166152e827eccfa88c17c602 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 2 Jun 2020 11:55:45 -0700
Subject: [PATCH 11/29] mypy

---
 opentelemetry-api/tests/test_implementation.py                 | 3 ++-
 .../src/opentelemetry/sdk/metrics/export/batcher.py            | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/opentelemetry-api/tests/test_implementation.py b/opentelemetry-api/tests/test_implementation.py
index 735ac4a683f..0dc37384ee9 100644
--- a/opentelemetry-api/tests/test_implementation.py
+++ b/opentelemetry-api/tests/test_implementation.py
@@ -83,7 +83,8 @@ def test_create_metric(self):
     def test_register_observer(self):
         meter = metrics.DefaultMeter()
         callback = mock.Mock()
-        observer = meter.register_observer(callback, "", "", "", int, (), True)
+        observer = meter.register_observer(
+            callback, "", "", "", int, metrics.ValueObserver)
         self.assertIsInstance(observer, metrics.DefaultObserver)
 
     def test_unregister_observer(self):
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index f5158e1a247..db3675ecd61 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -18,8 +18,8 @@
 from opentelemetry.metrics import (
     Counter,
     InstrumentT,
-    ValueRecorder,
     ValueObserver,
+    ValueRecorder,
 )
 from opentelemetry.sdk.metrics.export import MetricRecord
 from opentelemetry.sdk.metrics.export.aggregate import (

From 6e34921d265624b77c1234430bf07100dca407ea Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 2 Jun 2020 12:26:57 -0700
Subject: [PATCH 12/29] typing

---
 opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index 45176728f4d..58a43ea1336 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -378,7 +378,7 @@ def register_observer(
         observer_type=Type[metrics_api.ObserverT],
         label_keys: Sequence[str] = (),
         enabled: bool = True,
-    ) -> metrics_api.ObserverT:
+    ) -> metrics_api.Observer:
         ob = observer_type(
             callback,
             name,
@@ -393,7 +393,7 @@ def register_observer(
             self.observers.add(ob)
         return ob
 
-    def unregister_observer(self, observer: metrics_api.ObserverT) -> None:
+    def unregister_observer(self, observer: metrics_api.Observer) -> None:
         with self.observers_lock:
             self.observers.remove(observer)
 

From 2ee25855aede71225bc93a2128fe7ae372980061 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 2 Jun 2020 13:16:34 -0700
Subject: [PATCH 13/29] fix lint

---
 opentelemetry-api/tests/test_implementation.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/opentelemetry-api/tests/test_implementation.py b/opentelemetry-api/tests/test_implementation.py
index 0dc37384ee9..d0f9404a911 100644
--- a/opentelemetry-api/tests/test_implementation.py
+++ b/opentelemetry-api/tests/test_implementation.py
@@ -84,7 +84,8 @@ def test_register_observer(self):
         meter = metrics.DefaultMeter()
         callback = mock.Mock()
         observer = meter.register_observer(
-            callback, "", "", "", int, metrics.ValueObserver)
+            callback, "", "", "", int, metrics.ValueObserver
+        )
         self.assertIsInstance(observer, metrics.DefaultObserver)
 
     def test_unregister_observer(self):

From 677515a8baa0e1f2bec3b6d3a441a126b933bb28 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 2 Jun 2020 15:28:52 -0700
Subject: [PATCH 14/29] comment

---
 opentelemetry-api/src/opentelemetry/metrics/__init__.py | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/metrics/__init__.py b/opentelemetry-api/src/opentelemetry/metrics/__init__.py
index 81158f32e16..953a217d461 100644
--- a/opentelemetry-api/src/opentelemetry/metrics/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/metrics/__init__.py
@@ -253,8 +253,7 @@ def get_meter(
 
 MetricT = TypeVar("MetricT", Counter, ValueRecorder)
 InstrumentT = TypeVar("InstrumentT", Counter, Observer, ValueRecorder)
-# TODO: Will populate with other observers when implemented
-ObserverT = TypeVar("ObserverT", DefaultObserver, ValueObserver)
+ObserverT = TypeVar("ObserverT", bound=Observer)
 ObserverCallbackT = Callable[[Observer], None]
 
 
@@ -305,7 +304,6 @@ def create_metric(
             unit: Unit of the metric values following the UCUM convention
                 (https://unitsofmeasure.org/ucum.html).
             value_type: The type of values being recorded by the metric.
-            observer_type: The type of observer being registered.
             metric_type: The type of metric being created.
             label_keys: The keys for the labels with dynamic values.
             enabled: Whether to report the metric by default.
@@ -334,6 +332,7 @@ def register_observer(
             unit: Unit of the metric values following the UCUM convention
                 (https://unitsofmeasure.org/ucum.html).
             value_type: The type of values being recorded by the metric.
+            observer_type: The type of observer being registered.
             label_keys: The keys for the labels with dynamic values.
             enabled: Whether to report the metric by default.
         Returns: A new ``Observer`` metric instrument.

From 5061df9206037e9fd4b4f66d224d9d44320cf6f3 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 8 Jun 2020 12:36:24 -0700
Subject: [PATCH 15/29] sumobserver

---
 opentelemetry-api/CHANGELOG.md                |  4 +-
 .../src/opentelemetry/metrics/__init__.py     | 12 +++
 .../tests/metrics/test_metrics.py             | 10 ++-
 opentelemetry-sdk/CHANGELOG.md                |  2 +
 .../src/opentelemetry/sdk/metrics/__init__.py | 78 +++++++++++++++----
 .../sdk/metrics/export/aggregate.py           | 28 +++++++
 .../sdk/metrics/export/batcher.py             |  4 +
 .../tests/metrics/test_metrics.py             | 72 +++++++++++++++++
 8 files changed, 193 insertions(+), 17 deletions(-)

diff --git a/opentelemetry-api/CHANGELOG.md b/opentelemetry-api/CHANGELOG.md
index 3acfb90597e..ada8015a61b 100644
--- a/opentelemetry-api/CHANGELOG.md
+++ b/opentelemetry-api/CHANGELOG.md
@@ -2,10 +2,12 @@
 
 ## Unreleased
 
-- Rename Observer to ValueObserver
+- Rename Observer to ValueObserver in metrics
   ([#751](https://github.com/open-telemetry/opentelemetry-python/pull/751))
 - Rename Measure to ValueRecorder in metrics
   ([#761](https://github.com/open-telemetry/opentelemetry-python/pull/761))
+- Add SumObserver in metrics
+  ([#761](https://github.com/open-telemetry/opentelemetry-python/pull/761))
 
 ## 0.8b0
 
diff --git a/opentelemetry-api/src/opentelemetry/metrics/__init__.py b/opentelemetry-api/src/opentelemetry/metrics/__init__.py
index 953a217d461..62bac06f22c 100644
--- a/opentelemetry-api/src/opentelemetry/metrics/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/metrics/__init__.py
@@ -189,6 +189,18 @@ def observe(self, value: ValueT, labels: Dict[str, str]) -> None:
         """
 
 
+class SumObserver(Observer):
+    """No-op implementation of ``SumObserver``."""
+
+    def observe(self, value: ValueT, labels: Dict[str, str]) -> None:
+        """Captures ``value`` to the sumobserver.
+
+        Args:
+            value: The value to capture to this sumobserver metric.
+            labels: Labels associated to ``value``.
+        """
+
+
 class ValueObserver(Observer):
     """No-op implementation of ``ValueObserver``."""
 
diff --git a/opentelemetry-api/tests/metrics/test_metrics.py b/opentelemetry-api/tests/metrics/test_metrics.py
index 897c7492e42..4d42d361d4b 100644
--- a/opentelemetry-api/tests/metrics/test_metrics.py
+++ b/opentelemetry-api/tests/metrics/test_metrics.py
@@ -56,6 +56,14 @@ def test_bound_valuerecorder(self):
         bound_valuerecorder = metrics.BoundValueRecorder()
         bound_valuerecorder.record(1)
 
-    def test_observer(self):
+    def test_default_observer(self):
         observer = metrics.DefaultObserver()
         observer.observe(1, {})
+
+    def test_sum_observer(self):
+        observer = metrics.SumObserver()
+        observer.observe(1, {})
+
+    def test_value_observer(self):
+        observer = metrics.ValueObserver()
+        observer.observe(1, {})
diff --git a/opentelemetry-sdk/CHANGELOG.md b/opentelemetry-sdk/CHANGELOG.md
index d4b92fae1ce..545f443a386 100644
--- a/opentelemetry-sdk/CHANGELOG.md
+++ b/opentelemetry-sdk/CHANGELOG.md
@@ -6,6 +6,8 @@
   ([#751](https://github.com/open-telemetry/opentelemetry-python/pull/751))
 - Rename Measure to ValueRecorder in metrics
   ([#761](https://github.com/open-telemetry/opentelemetry-python/pull/761))
+- Add SumObserver in metrics
+  ([#761](https://github.com/open-telemetry/opentelemetry-python/pull/761))
 
 ## 0.8b0
 
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index 58a43ea1336..441a5831cf1 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -105,12 +105,16 @@ def record(self, value: metrics_api.ValueT) -> None:
 
 
 class Metric(metrics_api.Metric):
-    """Base class for all metric types.
-
-    Also known as metric instrument. This is the class that is used to
-    represent a metric that is to be continuously recorded and tracked. Each
-    metric has a set of bound metrics that are created from the metric. See
-    `BaseBoundInstrument` for information on bound metric instruments.
+    """Base class for all synchronous metric types.
+
+    This is the class that is used to represent a metric that is to be
+    synchronously recorded and tracked. Synchronous instruments are called
+    inside a request, meaning they have an associated distributed context
+    (i.e. Span context, correlation context). Multiple metric events may occur
+    for a synchronous instrument within a give collection interval.
+    
+    Each metric has a set of bound metrics that are created from the metric.
+    See `BaseBoundInstrument` for information on bound metric instruments.
     """
 
     BOUND_INSTR_TYPE = BaseBoundInstrument
@@ -190,9 +194,14 @@ def record(
     UPDATE_FUNCTION = record
 
 
-class ValueObserver(metrics_api.ValueObserver):
-    """See `opentelemetry.metrics.ValueObserver`."""
+class Observer(metrics_api.Observer):
+    """Base class for all asynchronous metric types.
 
+    Also known as Observers, observer metric instruments are asynchronous in
+    that they are reported by a callback, once per collection interval, and
+    lack context. They are permitted to report only one value per distinct
+    label set per period.
+    """
     def __init__(
         self,
         callback: metrics_api.ObserverCallbackT,
@@ -218,15 +227,10 @@ def __init__(
     def observe(
         self, value: metrics_api.ValueT, labels: Dict[str, str]
     ) -> None:
-        if not self.enabled:
-            return
-        if not isinstance(value, self.value_type):
-            logger.warning(
-                "Invalid value passed for %s.", self.value_type.__name__
-            )
+        key = get_labels_as_key(labels)
+        if not self._validate_observe(value, key):
             return
 
-        key = get_labels_as_key(labels)
         if key not in self.aggregators:
             # TODO: how to cleanup aggregators?
             self.aggregators[key] = self.meter.batcher.aggregator_for(
@@ -235,6 +239,20 @@ def observe(
         aggregator = self.aggregators[key]
         aggregator.update(value)
 
+    def _validate_observe(self,
+        value: metrics_api.ValueT,
+        key: Tuple[Tuple[str, str]],
+    ):
+        if not self.enabled:
+            return False
+        if not isinstance(value, self.value_type):
+            logger.warning(
+                "Invalid value passed for %s.", self.value_type.__name__
+            )
+            return False
+
+        return True
+
     def run(self) -> bool:
         try:
             self.callback(self)
@@ -252,6 +270,36 @@ def __repr__(self):
         )
 
 
+class SumObserver(Observer, metrics_api.SumObserver):
+    """See `opentelemetry.metrics.SumObserver`."""
+
+    def _validate_observe(self,
+        value: metrics_api.ValueT,
+        key: Tuple[Tuple[str, str]],
+    ):
+        if super()._validate_observe(value, key):
+            # Must be non-decreasing because monotonic
+            if key in self.aggregators and \
+                self.aggregators[key].current is not None:
+                if value < self.aggregators[key].current:
+                    logger.warning(
+                        "Value passed must be non-decreasing."
+                    )
+                    return False
+            return True
+        return False
+
+
+class ValueObserver(Observer, metrics_api.ValueObserver):
+    """See `opentelemetry.metrics.ValueObserver`."""
+
+    def _validate_observe(self,
+        value: metrics_api.ValueT,
+        key: Tuple[Tuple[str, str]],
+    ):
+        return super()._validate_observe(value, key)
+
+
 class Record:
     """Container class used for processing in the `Batcher`"""
 
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py
index 1745d854e9d..ad728d8c502 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py
@@ -125,6 +125,34 @@ def merge(self, other):
             )
 
 
+class LastValueAggregator(Aggregator):
+    """Aggregator that stores last value results."""
+
+    def __init__(self):
+        super().__init__()
+        self._lock = threading.Lock()
+        self.last_update_timestamp = None
+
+    def update(self, value):
+        with self._lock:
+            self.current = value
+            self.last_update_timestamp = time_ns()
+
+    def take_checkpoint(self):
+        with self._lock:
+            self.checkpoint = self.current
+            self.current = None
+
+    def merge(self, other):
+        last = self.checkpoint.last
+        self.last_update_timestamp = get_latest_timestamp(
+            self.last_update_timestamp, other.last_update_timestamp
+        )
+        if self.last_update_timestamp == other.last_update_timestamp:
+            last = other.checkpoint.last
+        self.checkpoint = last
+
+
 class ValueObserverAggregator(Aggregator):
     """Same as MinMaxSumCount but also with last value."""
 
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index db3675ecd61..f3bc91b0602 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -18,6 +18,7 @@
 from opentelemetry.metrics import (
     Counter,
     InstrumentT,
+    SumObserver,
     ValueObserver,
     ValueRecorder,
 )
@@ -25,6 +26,7 @@
 from opentelemetry.sdk.metrics.export.aggregate import (
     Aggregator,
     CounterAggregator,
+    LastValueAggregator,
     MinMaxSumCountAggregator,
     ValueObserverAggregator,
 )
@@ -54,6 +56,8 @@ def aggregator_for(self, instrument_type: Type[InstrumentT]) -> Aggregator:
         # pylint:disable=R0201
         if issubclass(instrument_type, Counter):
             return CounterAggregator()
+        if issubclass(instrument_type, SumObserver):
+            return LastValueAggregator()
         if issubclass(instrument_type, ValueRecorder):
             return MinMaxSumCountAggregator()
         if issubclass(instrument_type, ValueObserver):
diff --git a/opentelemetry-sdk/tests/metrics/test_metrics.py b/opentelemetry-sdk/tests/metrics/test_metrics.py
index d4d48ff06ec..bc9c2918206 100644
--- a/opentelemetry-sdk/tests/metrics/test_metrics.py
+++ b/opentelemetry-sdk/tests/metrics/test_metrics.py
@@ -285,6 +285,78 @@ def test_record(self):
         )
 
 
+class TestSumObserver(unittest.TestCase):
+    def test_observe(self):
+        meter = metrics.MeterProvider().get_meter(__name__)
+        observer = metrics.SumObserver(
+            None, "name", "desc", "unit", int, meter, ("key",), True
+        )
+        labels = {"key": "value"}
+        key_labels = tuple(sorted(labels.items()))
+        values = (37, 42, 60, 100)
+        for val in values:
+            observer.observe(val, labels)
+
+        self.assertEqual(observer.aggregators[key_labels].current, values[-1])
+
+    def test_observe_disabled(self):
+        meter = metrics.MeterProvider().get_meter(__name__)
+        observer = metrics.SumObserver(
+            None, "name", "desc", "unit", int, meter, ("key",), False
+        )
+        labels = {"key": "value"}
+        observer.observe(37, labels)
+        self.assertEqual(len(observer.aggregators), 0)
+
+    @mock.patch("opentelemetry.sdk.metrics.logger")
+    def test_observe_incorrect_type(self, logger_mock):
+        meter = metrics.MeterProvider().get_meter(__name__)
+        observer = metrics.SumObserver(
+            None, "name", "desc", "unit", int, meter, ("key",), True
+        )
+        labels = {"key": "value"}
+        observer.observe(37.0, labels)
+        self.assertEqual(len(observer.aggregators), 0)
+        self.assertTrue(logger_mock.warning.called)
+
+    @mock.patch("opentelemetry.sdk.metrics.logger")
+    def test_observe_non_decreasing_error(self, logger_mock):
+        meter = metrics.MeterProvider().get_meter(__name__)
+        observer = metrics.SumObserver(
+            None, "name", "desc", "unit", int, meter, ("key",), True
+        )
+        labels = {"key": "value"}
+        observer.observe(37, labels)
+        observer.observe(14, labels)
+        self.assertEqual(len(observer.aggregators), 1)
+        self.assertTrue(logger_mock.warning.called)
+
+    def test_run(self):
+        meter = metrics.MeterProvider().get_meter(__name__)
+
+        callback = mock.Mock()
+        observer = metrics.SumObserver(
+            callback, "name", "desc", "unit", int, meter, (), True
+        )
+
+        self.assertTrue(observer.run())
+        callback.assert_called_once_with(observer)
+
+    @mock.patch("opentelemetry.sdk.metrics.logger")
+    def test_run_exception(self, logger_mock):
+        meter = metrics.MeterProvider().get_meter(__name__)
+
+        callback = mock.Mock()
+        callback.side_effect = Exception("We have a problem!")
+
+        observer = metrics.SumObserver(
+            callback, "name", "desc", "unit", int, meter, (), True
+        )
+
+        self.assertFalse(observer.run())
+        self.assertTrue(logger_mock.warning.called)
+
+
 class TestValueObserver(unittest.TestCase):
     def test_observe(self):
         meter = metrics.MeterProvider().get_meter(__name__)

From 9f1081574bcbd20aa16cfc74314c756b18489bbf Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 8 Jun 2020 12:47:27 -0700
Subject: [PATCH 16/29] changelog

---
 opentelemetry-api/CHANGELOG.md | 2 +-
 opentelemetry-sdk/CHANGELOG.md | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/opentelemetry-api/CHANGELOG.md b/opentelemetry-api/CHANGELOG.md
index cbce5f59bc7..88c9c4b9671 100644
--- a/opentelemetry-api/CHANGELOG.md
+++ b/opentelemetry-api/CHANGELOG.md
@@ -9,7 +9,7 @@
 - Rename Observer to ValueObserver
   ([#764](https://github.com/open-telemetry/opentelemetry-python/pull/764))
 - Add SumObserver in metrics
-  ([#761](https://github.com/open-telemetry/opentelemetry-python/pull/761))
+  ([#789](https://github.com/open-telemetry/opentelemetry-python/pull/789))
 
 ## 0.8b0
 
diff --git a/opentelemetry-sdk/CHANGELOG.md b/opentelemetry-sdk/CHANGELOG.md
index 819f7a2caf5..447bce245f5 100644
--- a/opentelemetry-sdk/CHANGELOG.md
+++ b/opentelemetry-sdk/CHANGELOG.md
@@ -11,7 +11,7 @@
 - Rename Observer to ValueObserver
   ([#764](https://github.com/open-telemetry/opentelemetry-python/pull/764))
 - Add SumObserver in metrics
-  ([#761](https://github.com/open-telemetry/opentelemetry-python/pull/761))
+  ([#789](https://github.com/open-telemetry/opentelemetry-python/pull/789))
 
 ## 0.8b0
 

From a18ee9589df912ad3537e28347cdfa67d4abc9fe Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 8 Jun 2020 13:36:04 -0700
Subject: [PATCH 17/29] lint

---
 .../src/opentelemetry/sdk/metrics/__init__.py | 26 +++++++++----------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index a0949897e7c..f2e1f97c7b5 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -202,6 +202,7 @@ class Observer(metrics_api.Observer):
     lack context. They are permitted to report only one value per distinct
     label set per period.
     """
+
     def __init__(
         self,
         callback: metrics_api.ObserverCallbackT,
@@ -239,9 +240,8 @@ def observe(
         aggregator = self.aggregators[key]
         aggregator.update(value)
 
-    def _validate_observe(self,
-        value: metrics_api.ValueT,
-        key: Tuple[Tuple[str, str]],
+    def _validate_observe(
+        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]],
     ):
         if not self.enabled:
             return False
@@ -273,18 +273,17 @@ def __repr__(self):
 class SumObserver(Observer, metrics_api.SumObserver):
     """See `opentelemetry.metrics.SumObserver`."""
 
-    def _validate_observe(self,
-        value: metrics_api.ValueT,
-        key: Tuple[Tuple[str, str]],
+    def _validate_observe(
+        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]],
     ):
         if super()._validate_observe(value, key):
             # Must be non-decreasing because monotonic
-            if key in self.aggregators and \
-                self.aggregators[key].current is not None:
+            if (
+                key in self.aggregators
+                and self.aggregators[key].current is not None
+            ):
                 if value < self.aggregators[key].current:
-                    logger.warning(
-                        "Value passed must be non-decreasing."
-                    )
+                    logger.warning("Value passed must be non-decreasing.")
                     return False
             return True
         return False
@@ -293,9 +292,8 @@ def _validate_observe(self,
 class ValueObserver(Observer, metrics_api.ValueObserver):
     """See `opentelemetry.metrics.ValueObserver`."""
 
-    def _validate_observe(self,
-        value: metrics_api.ValueT,
-        key: Tuple[Tuple[str, str]],
+    def _validate_observe(
+        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]],
     ):
         return super()._validate_observe(value, key)
 

From edb310d2910b650c7895cccaa5158266a5e28c45 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 8 Jun 2020 14:15:27 -0700
Subject: [PATCH 18/29] lint

---
 opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index f2e1f97c7b5..d531e79e258 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -112,7 +112,7 @@ class Metric(metrics_api.Metric):
     inside a request, meaning they have an associated distributed context
     (i.e. Span context, correlation context). Multiple metric events may occur
     for a synchronous instrument within a give collection interval.
-    
+
     Each metric has a set of bound metrics that are created from the metric.
     See `BaseBoundInstrument` for information on bound metric instruments.
     """

From 5c67c2ac2af205d53d601b39553ae8923ec55e76 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 8 Jun 2020 14:37:50 -0700
Subject: [PATCH 19/29] lint

---
 .../src/opentelemetry/sdk/metrics/__init__.py        | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index d531e79e258..20545dd1384 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -240,8 +240,11 @@ def observe(
         aggregator = self.aggregators[key]
         aggregator.update(value)
 
+    # pylint: disable=W0613
     def _validate_observe(
-        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]],
+        self,
+        value: metrics_api.ValueT,
+        key: Tuple[Tuple[str, str]] = None,
     ):
         if not self.enabled:
             return False
@@ -274,7 +277,9 @@ class SumObserver(Observer, metrics_api.SumObserver):
     """See `opentelemetry.metrics.SumObserver`."""
 
     def _validate_observe(
-        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]],
+        self,
+        value: metrics_api.ValueT,
+        key: Tuple[Tuple[str, str]],
     ):
         if super()._validate_observe(value, key):
             # Must be non-decreasing because monotonic
@@ -292,8 +297,9 @@ def _validate_observe(
 class ValueObserver(Observer, metrics_api.ValueObserver):
     """See `opentelemetry.metrics.ValueObserver`."""
 
+    # pylint: disable=W0235
     def _validate_observe(
-        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]],
+        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]] = None,
     ):
         return super()._validate_observe(value, key)
 

From ce333713da9a2eb291d8245ca585b38ed9be50bc Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 8 Jun 2020 15:17:42 -0700
Subject: [PATCH 20/29] black

---
 .../src/opentelemetry/sdk/metrics/__init__.py             | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index 20545dd1384..d21a69e3527 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -242,9 +242,7 @@ def observe(
 
     # pylint: disable=W0613
     def _validate_observe(
-        self,
-        value: metrics_api.ValueT,
-        key: Tuple[Tuple[str, str]] = None,
+        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]] = None,
     ):
         if not self.enabled:
             return False
@@ -277,9 +275,7 @@ class SumObserver(Observer, metrics_api.SumObserver):
     """See `opentelemetry.metrics.SumObserver`."""
 
     def _validate_observe(
-        self,
-        value: metrics_api.ValueT,
-        key: Tuple[Tuple[str, str]],
+        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]],
     ):
         if super()._validate_observe(value, key):
             # Must be non-decreasing because monotonic

From aa0007b6c00e7d17c11d0ad3a3bd62acb32cd709 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 8 Jun 2020 16:09:37 -0700
Subject: [PATCH 21/29] lint

---
 opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index d21a69e3527..3928b8068f6 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -275,12 +275,13 @@ class SumObserver(Observer, metrics_api.SumObserver):
     """See `opentelemetry.metrics.SumObserver`."""
 
     def _validate_observe(
-        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]],
+        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]] = None,
     ):
         if super()._validate_observe(value, key):
             # Must be non-decreasing because monotonic
             if (
-                key in self.aggregators
+                key is not None
+                and key in self.aggregators
                 and self.aggregators[key].current is not None
             ):
                 if value < self.aggregators[key].current:

From f33e7e4234b20dfd20fa3ef479bbe1da01cf0892 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 8 Jun 2020 22:09:15 -0700
Subject: [PATCH 22/29] fix example

---
 docs/examples/basic_meter/observer.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/docs/examples/basic_meter/observer.py b/docs/examples/basic_meter/observer.py
index b61b9e4db80..d3aa02168d4 100644
--- a/docs/examples/basic_meter/observer.py
+++ b/docs/examples/basic_meter/observer.py
@@ -60,6 +60,7 @@ def get_ram_usage_callback(observer):
     description="RAM memory usage",
     unit="1",
     value_type=float,
+    observer_type=ValueObserver,
     label_keys=(),
 )
 

From 541a11cbdd333aed15b6fe07f6c8d3c345435ef3 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 8 Jun 2020 22:50:44 -0700
Subject: [PATCH 23/29] updownobserver

---
 .../src/opentelemetry/metrics/__init__.py     | 12 ++++
 .../tests/metrics/test_metrics.py             |  4 ++
 opentelemetry-sdk/CHANGELOG.md                |  2 +-
 .../src/opentelemetry/sdk/metrics/__init__.py | 10 ++++
 .../sdk/metrics/export/batcher.py             |  4 +-
 .../tests/metrics/test_metrics.py             | 60 +++++++++++++++++++
 6 files changed, 90 insertions(+), 2 deletions(-)

diff --git a/opentelemetry-api/src/opentelemetry/metrics/__init__.py b/opentelemetry-api/src/opentelemetry/metrics/__init__.py
index 93289c019b3..569930d6f3b 100644
--- a/opentelemetry-api/src/opentelemetry/metrics/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/metrics/__init__.py
@@ -201,6 +201,18 @@ def observe(self, value: ValueT, labels: Dict[str, str]) -> None:
         """
 
 
+class UpDownSumObserver(Observer):
+    """No-op implementation of ``UpDownSumObserver``."""
+
+    def observe(self, value: ValueT, labels: Dict[str, str]) -> None:
+        """Captures ``value`` to the updownsumobserver.
+
+        Args:
+            value: The value to capture to this updownsumobserver metric.
+            labels: Labels associated to ``value``.
+        """
+
+
 class ValueObserver(Observer):
     """No-op implementation of ``ValueObserver``."""
 
diff --git a/opentelemetry-api/tests/metrics/test_metrics.py b/opentelemetry-api/tests/metrics/test_metrics.py
index 4d42d361d4b..b3cbdefd15a 100644
--- a/opentelemetry-api/tests/metrics/test_metrics.py
+++ b/opentelemetry-api/tests/metrics/test_metrics.py
@@ -64,6 +64,10 @@ def test_sum_observer(self):
         observer = metrics.SumObserver()
         observer.observe(1, {})
 
+    def test_updown_sum_observer(self):
+        observer = metrics.UpDownSumObserver()
+        observer.observe(1, {})
+
     def test_value_observer(self):
         observer = metrics.ValueObserver()
         observer.observe(1, {})
diff --git a/opentelemetry-sdk/CHANGELOG.md b/opentelemetry-sdk/CHANGELOG.md
index 447bce245f5..6213e31ae61 100644
--- a/opentelemetry-sdk/CHANGELOG.md
+++ b/opentelemetry-sdk/CHANGELOG.md
@@ -10,7 +10,7 @@
   ([#775](https://github.com/open-telemetry/opentelemetry-python/pull/775))
 - Rename Observer to ValueObserver
   ([#764](https://github.com/open-telemetry/opentelemetry-python/pull/764))
-- Add SumObserver in metrics
+- Add SumObserver and UpDownSumObserver in metrics
   ([#789](https://github.com/open-telemetry/opentelemetry-python/pull/789))
 
 ## 0.8b0
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index 3928b8068f6..909b16b1698 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -291,6 +291,16 @@ def _validate_observe(
         return False
 
 
+class UpDownSumObserver(Observer, metrics_api.UpDownSumObserver):
+    """See `opentelemetry.metrics.UpDownSumObserver`."""
+
+    # pylint: disable=W0235
+    def _validate_observe(
+        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]] = None,
+    ):
+        return super()._validate_observe(value, key)
+
+
 class ValueObserver(Observer, metrics_api.ValueObserver):
     """See `opentelemetry.metrics.ValueObserver`."""
 
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index f3bc91b0602..a3cb5ef65b0 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -19,6 +19,7 @@
     Counter,
     InstrumentT,
     SumObserver,
+    UpDownSumObserver,
     ValueObserver,
     ValueRecorder,
 )
@@ -56,7 +57,8 @@ def aggregator_for(self, instrument_type: Type[InstrumentT]) -> Aggregator:
         # pylint:disable=R0201
         if issubclass(instrument_type, Counter):
             return CounterAggregator()
-        if issubclass(instrument_type, SumObserver):
+        if issubclass(instrument_type, SumObserver) or \
+            issubclass(instrument_type, UpDownSumObserver):
             return LastValueAggregator()
         if issubclass(instrument_type, ValueRecorder):
             return MinMaxSumCountAggregator()
diff --git a/opentelemetry-sdk/tests/metrics/test_metrics.py b/opentelemetry-sdk/tests/metrics/test_metrics.py
index 8a616e1da97..02cf2c93548 100644
--- a/opentelemetry-sdk/tests/metrics/test_metrics.py
+++ b/opentelemetry-sdk/tests/metrics/test_metrics.py
@@ -362,6 +362,66 @@ def test_run_exception(self, logger_mock):
         self.assertTrue(logger_mock.warning.called)
 
 
+class TestUpDownSumObserver(unittest.TestCase):
+    def test_observe(self):
+        meter = metrics.MeterProvider().get_meter(__name__)
+        observer = metrics.UpDownSumObserver(
+            None, "name", "desc", "unit", int, meter, ("key",), True
+        )
+        labels = {"key": "value"}
+        key_labels = tuple(sorted(labels.items()))
+        values = (37, 42, 14, 30)
+        for val in values:
+            observer.observe(val, labels)
+
+        self.assertEqual(observer.aggregators[key_labels].current, values[-1])
+
+    def test_observe_disabled(self):
+        meter = metrics.MeterProvider().get_meter(__name__)
+        observer = metrics.UpDownSumObserver(
+            None, "name", "desc", "unit", int, meter, ("key",), False
+        )
+        labels = {"key": "value"}
+        observer.observe(37, labels)
+        self.assertEqual(len(observer.aggregators), 0)
+
+    @mock.patch("opentelemetry.sdk.metrics.logger")
+    def test_observe_incorrect_type(self, logger_mock):
+        meter = metrics.MeterProvider().get_meter(__name__)
+        observer = metrics.UpDownSumObserver(
+            None, "name", "desc", "unit", int, meter, ("key",), True
+        )
+        labels = {"key": "value"}
+        observer.observe(37.0, labels)
+        self.assertEqual(len(observer.aggregators), 0)
+        self.assertTrue(logger_mock.warning.called)
+
+    def test_run(self):
+        meter = metrics.MeterProvider().get_meter(__name__)
+
+        callback = mock.Mock()
+        observer = metrics.UpDownSumObserver(
+            callback, "name", "desc", "unit", int, meter, (), True
+        )
+
+        self.assertTrue(observer.run())
+        callback.assert_called_once_with(observer)
+
+    @mock.patch("opentelemetry.sdk.metrics.logger")
+    def test_run_exception(self, logger_mock):
+        meter = metrics.MeterProvider().get_meter(__name__)
+
+        callback = mock.Mock()
+        callback.side_effect = Exception("We have a problem!")
+
+        observer = metrics.UpDownSumObserver(
+            callback, "name", "desc", "unit", int, meter, (), True
+        )
+
+        self.assertFalse(observer.run())
+        self.assertTrue(logger_mock.warning.called)
+
+
 class TestValueObserver(unittest.TestCase):
     def test_observe(self):
         meter = metrics.MeterProvider().get_meter(__name__)

From e9489c7dcd27de28b2ba70daea17c209947b9e8c Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Mon, 8 Jun 2020 23:19:30 -0700
Subject: [PATCH 24/29] lint

---
 .../src/opentelemetry/sdk/metrics/export/batcher.py          | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index a3cb5ef65b0..e4b5b42697d 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -57,8 +57,9 @@ def aggregator_for(self, instrument_type: Type[InstrumentT]) -> Aggregator:
         # pylint:disable=R0201
         if issubclass(instrument_type, Counter):
             return CounterAggregator()
-        if issubclass(instrument_type, SumObserver) or \
-            issubclass(instrument_type, UpDownSumObserver):
+        if issubclass(instrument_type, SumObserver) or issubclass(
+            instrument_type, UpDownSumObserver
+        ):
             return LastValueAggregator()
         if issubclass(instrument_type, ValueRecorder):
             return MinMaxSumCountAggregator()

From f1a276703a44d04cc086bcfd8436d2db83c0e761 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 9 Jun 2020 14:11:29 -0700
Subject: [PATCH 25/29] address comments

---
 .../src/opentelemetry/sdk/metrics/__init__.py | 46 ++++++++-----------
 .../sdk/metrics/export/batcher.py             |  4 +-
 2 files changed, 19 insertions(+), 31 deletions(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index 909b16b1698..92a68caf664 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -242,8 +242,8 @@ def observe(
 
     # pylint: disable=W0613
     def _validate_observe(
-        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]] = None,
-    ):
+        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]],
+    ) -> bool:
         if not self.enabled:
             return False
         if not isinstance(value, self.value_type):
@@ -275,40 +275,30 @@ class SumObserver(Observer, metrics_api.SumObserver):
     """See `opentelemetry.metrics.SumObserver`."""
 
     def _validate_observe(
-        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]] = None,
-    ):
-        if super()._validate_observe(value, key):
-            # Must be non-decreasing because monotonic
-            if (
-                key is not None
-                and key in self.aggregators
-                and self.aggregators[key].current is not None
-            ):
-                if value < self.aggregators[key].current:
-                    logger.warning("Value passed must be non-decreasing.")
-                    return False
-            return True
-        return False
+        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]],
+    ) -> bool:
+        if not super()._validate_observe(value, key):
+            return False
+        # Must be non-decreasing because monotonic
+        if (
+            key in self.aggregators
+            and self.aggregators[key].current is not None
+        ):
+            if value < self.aggregators[key].current:
+                logger.warning("Value passed must be non-decreasing.")
+                return False
+        return True
+
 
 
 class UpDownSumObserver(Observer, metrics_api.UpDownSumObserver):
     """See `opentelemetry.metrics.UpDownSumObserver`."""
-
-    # pylint: disable=W0235
-    def _validate_observe(
-        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]] = None,
-    ):
-        return super()._validate_observe(value, key)
+    pass
 
 
 class ValueObserver(Observer, metrics_api.ValueObserver):
     """See `opentelemetry.metrics.ValueObserver`."""
-
-    # pylint: disable=W0235
-    def _validate_observe(
-        self, value: metrics_api.ValueT, key: Tuple[Tuple[str, str]] = None,
-    ):
-        return super()._validate_observe(value, key)
+    pass
 
 
 class Record:
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
index e4b5b42697d..c0405d1ffb8 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py
@@ -57,9 +57,7 @@ def aggregator_for(self, instrument_type: Type[InstrumentT]) -> Aggregator:
         # pylint:disable=R0201
         if issubclass(instrument_type, Counter):
             return CounterAggregator()
-        if issubclass(instrument_type, SumObserver) or issubclass(
-            instrument_type, UpDownSumObserver
-        ):
+        if issubclass(instrument_type, (SumObserver, UpDownSumObserver)):
             return LastValueAggregator()
         if issubclass(instrument_type, ValueRecorder):
             return MinMaxSumCountAggregator()

From 168c874f552107933c38485ff7e5ec8bc5ba8a35 Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 9 Jun 2020 14:33:41 -0700
Subject: [PATCH 26/29] black

---
 opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index 92a68caf664..cab6d8ae607 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -290,14 +290,15 @@ def _validate_observe(
         return True
 
 
-
 class UpDownSumObserver(Observer, metrics_api.UpDownSumObserver):
     """See `opentelemetry.metrics.UpDownSumObserver`."""
+
     pass
 
 
 class ValueObserver(Observer, metrics_api.ValueObserver):
     """See `opentelemetry.metrics.ValueObserver`."""
+
     pass
 
 

From 5a37c0ceacf08c454d71b479612a57b8008046aa Mon Sep 17 00:00:00 2001
From: Leighton Chen <lechen@microsoft.com>
Date: Tue, 9 Jun 2020 15:09:17 -0700
Subject: [PATCH 27/29] Update opentelemetry-api/CHANGELOG.md

Co-authored-by: alrex <alrex.boten@gmail.com>
---
 opentelemetry-api/CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/opentelemetry-api/CHANGELOG.md b/opentelemetry-api/CHANGELOG.md
index 1862c23093d..670e3d7a7f5 100644
--- a/opentelemetry-api/CHANGELOG.md
+++ b/opentelemetry-api/CHANGELOG.md
@@ -10,7 +10,7 @@
   ([#552](https://github.com/open-telemetry/opentelemetry-python/pull/552))
 - Rename Observer to ValueObserver
   ([#764](https://github.com/open-telemetry/opentelemetry-python/pull/764))
-- Add SumObserver in metrics
+- Add SumObserver and UpDownSumObserver in metrics
   ([#789](https://github.com/open-telemetry/opentelemetry-python/pull/789))
 
 ## 0.8b0

From 5463add632d5667dd640833ce81b3ea32dc42012 Mon Sep 17 00:00:00 2001
From: Leighton Chen <lechen@microsoft.com>
Date: Tue, 9 Jun 2020 15:09:26 -0700
Subject: [PATCH 28/29] Update opentelemetry-sdk/CHANGELOG.md

Co-authored-by: alrex <alrex.boten@gmail.com>
---
 opentelemetry-sdk/CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/opentelemetry-sdk/CHANGELOG.md b/opentelemetry-sdk/CHANGELOG.md
index fdb7bc6810e..23007dde5a8 100644
--- a/opentelemetry-sdk/CHANGELOG.md
+++ b/opentelemetry-sdk/CHANGELOG.md
@@ -12,7 +12,7 @@
   ([#775](https://github.com/open-telemetry/opentelemetry-python/pull/775))
 - Rename Observer to ValueObserver
   ([#764](https://github.com/open-telemetry/opentelemetry-python/pull/764))
-- Add SumObserver and UpDownSumObserver in metrics
+- Add SumObserver, UpDownSumObserver and LastValueAggregator in metrics
   ([#789](https://github.com/open-telemetry/opentelemetry-python/pull/789))
 
 ## 0.8b0

From 9de59a9a164777a28db56dc593190350d7c8673b Mon Sep 17 00:00:00 2001
From: Leighton <lechen@microsoft.com>
Date: Tue, 9 Jun 2020 15:09:45 -0700
Subject: [PATCH 29/29] lint

---
 opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
index cab6d8ae607..7156f68c165 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/metrics/__init__.py
@@ -293,14 +293,10 @@ def _validate_observe(
 class UpDownSumObserver(Observer, metrics_api.UpDownSumObserver):
     """See `opentelemetry.metrics.UpDownSumObserver`."""
 
-    pass
-
 
 class ValueObserver(Observer, metrics_api.ValueObserver):
     """See `opentelemetry.metrics.ValueObserver`."""
 
-    pass
-
 
 class Record:
     """Container class used for processing in the `Batcher`"""