From de3ca876d9a42a09b109e4752c43db06b1048d59 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Thu, 24 Sep 2020 13:49:14 +0200
Subject: [PATCH 1/6] ARROW-9518: [Python] Deprecate pyarrow serialization

---
 python/pyarrow/_plasma.pyx                 | 18 ++++++--
 python/pyarrow/serialization.pxi           | 53 ++++++++++++++++++++--
 python/pyarrow/serialization.py            |  7 +++
 python/pyarrow/tests/test_pandas.py        |  9 ++--
 python/pyarrow/tests/test_serialization.py |  6 ++-
 5 files changed, 83 insertions(+), 10 deletions(-)

diff --git a/python/pyarrow/_plasma.pyx b/python/pyarrow/_plasma.pyx
index 157fa7a4d79..5cab1030169 100644
--- a/python/pyarrow/_plasma.pyx
+++ b/python/pyarrow/_plasma.pyx
@@ -535,7 +535,13 @@ cdef class PlasmaClient(_Weakrefable):
         """
         cdef ObjectID target_id = (object_id if object_id
                                    else ObjectID.from_random())
-        serialized = pyarrow.serialize(value, serialization_context)
+        if serialization_context is not None:
+            warnings.warn(
+                "'serialization_context' is deprecated and will be removed "
+                "in a future version.",
+                DeprecationWarning, stacklevel=2
+            )
+        serialized = pyarrow.lib._serialize(value, serialization_context)
         buffer = self.create(target_id, serialized.total_bytes)
         stream = pyarrow.FixedSizeBufferWriter(buffer)
         stream.set_memcopy_threads(memcopy_threads)
@@ -566,6 +572,12 @@ cdef class PlasmaClient(_Weakrefable):
             the object_ids and ObjectNotAvailable if the object was not
             available.
         """
+        if serialization_context is not None:
+            warnings.warn(
+                "'serialization_context' is deprecated and will be removed "
+                "in a future version.",
+                DeprecationWarning, stacklevel=2
+            )
         if isinstance(object_ids, Sequence):
             results = []
             buffers = self.get_buffers(object_ids, timeout_ms)
@@ -573,8 +585,8 @@ cdef class PlasmaClient(_Weakrefable):
                 # buffers[i] is None if this object was not available within
                 # the timeout
                 if buffers[i]:
-                    val = pyarrow.deserialize(buffers[i],
-                                              serialization_context)
+                    val = pyarrow.lib._deserialize(buffers[i],
+                                                   serialization_context)
                     results.append(val)
                 else:
                     results.append(ObjectNotAvailable)
diff --git a/python/pyarrow/serialization.pxi b/python/pyarrow/serialization.pxi
index ee999b5aa8b..10c7eef74cc 100644
--- a/python/pyarrow/serialization.pxi
+++ b/python/pyarrow/serialization.pxi
@@ -17,6 +17,8 @@
 
 from cpython.ref cimport PyObject
 
+import warnings
+
 
 def is_named_tuple(cls):
     """
@@ -43,6 +45,7 @@ class DeserializationCallbackError(ArrowSerializationError):
         self.type_id = type_id
 
 
+# TODO deprecate accessing this class top-level
 cdef class SerializationContext(_Weakrefable):
     cdef:
         object type_to_type_id
@@ -369,6 +372,15 @@ def serialize(object value, SerializationContext context=None):
     serialized : SerializedPyObject
 
     """
+    warnings.warn(
+        "'pyarrow.serialize' is deprecated and will be removed in a future "
+        "version. Use pickle or the pyarrow IPC functionality instead.",
+        DeprecationWarning, stacklevel=2
+    )
+    return _serialize(value, context)
+
+
+def _serialize(object value, SerializationContext context=None):
     cdef SerializedPyObject serialized = SerializedPyObject()
     wrapped_value = [value]
 
@@ -394,7 +406,12 @@ def serialize_to(object value, sink, SerializationContext context=None):
         Custom serialization and deserialization context, uses a default
         context with some standard type handlers if not specified.
     """
-    serialized = serialize(value, context)
+    warnings.warn(
+        "'pyarrow.serialize_to' is deprecated and will be removed in a future "
+        "version. Use pickle or the pyarrow IPC functionality instead.",
+        DeprecationWarning, stacklevel=2
+    )
+    serialized = _serialize(value, context)
     serialized.write_to(sink)
 
 
@@ -414,6 +431,15 @@ def read_serialized(source, base=None):
     -------
     serialized : the serialized data
     """
+    warnings.warn(
+        "'pyarrow.read_serialized' is deprecated and will be removed in a "
+        "future version. Use pickle or the pyarrow IPC functionality instead.",
+        DeprecationWarning, stacklevel=2
+    )
+    return _read_serialized(source, base=base)
+
+
+def _read_serialized(source, base=None):
     cdef shared_ptr[CRandomAccessFile] stream
     get_reader(source, True, &stream)
 
@@ -447,7 +473,12 @@ def deserialize_from(source, object base, SerializationContext context=None):
     object
         Python object for the deserialized sequence.
     """
-    serialized = read_serialized(source, base=base)
+    warnings.warn(
+        "'pyarrow.deserialize_from' is deprecated and will be removed in a "
+        "future version. Use pickle or the pyarrow IPC functionality instead.",
+        DeprecationWarning, stacklevel=2
+    )
+    serialized = _read_serialized(source, base=base)
     return serialized.deserialize(context)
 
 
@@ -465,6 +496,12 @@ def deserialize_components(components, SerializationContext context=None):
     -------
     object : the Python object that was originally serialized
     """
+    warnings.warn(
+        "'pyarrow.deserialize_components' is deprecated and will be removed "
+        "in a future version. Use pickle or the pyarrow IPC functionality "
+        "instead.",
+        DeprecationWarning, stacklevel=2
+    )
     serialized = SerializedPyObject.from_components(components)
     return serialized.deserialize(context)
 
@@ -487,5 +524,15 @@ def deserialize(obj, SerializationContext context=None):
     -------
     deserialized : object
     """
+    warnings.warn(
+        "'pyarrow.deserialize' is deprecated and will be removed in a future "
+        "version. Use pickle or the pyarrow IPC functionality instead.",
+        DeprecationWarning, stacklevel=2
+    )
+    return _deserialize(obj, context=context)
+
+
+def _deserialize(obj, SerializationContext context=None):
     source = BufferReader(obj)
-    return deserialize_from(source, obj, context)
+    serialized = _read_serialized(source, base=obj)
+    return serialized.deserialize(context)
diff --git a/python/pyarrow/serialization.py b/python/pyarrow/serialization.py
index 9c1d53ea646..408ae7c7185 100644
--- a/python/pyarrow/serialization.py
+++ b/python/pyarrow/serialization.py
@@ -16,6 +16,7 @@
 # under the License.
 
 import collections
+import warnings
 
 import numpy as np
 
@@ -483,6 +484,12 @@ def register_default_serialization_handlers(serialization_context):
 
 
 def default_serialization_context():
+    warnings.warn(
+        "'pyarrow.default_serialization_context' is deprecated and will be "
+        "removed in a future version. Use pickle or the pyarrow IPC "
+        "functionality instead.",
+        DeprecationWarning, stacklevel=2
+    )
     context = SerializationContext()
     register_default_serialization_handlers(context)
     return context
diff --git a/python/pyarrow/tests/test_pandas.py b/python/pyarrow/tests/test_pandas.py
index 0e01dc08ef6..41b76339782 100644
--- a/python/pyarrow/tests/test_pandas.py
+++ b/python/pyarrow/tests/test_pandas.py
@@ -2764,10 +2764,13 @@ def test_roundtrip_with_bytes_unicode(columns):
 
 
 def _check_serialize_components_roundtrip(pd_obj):
-    ctx = pa.default_serialization_context()
+    with pytest.warns(DeprecationWarning):
+        ctx = pa.default_serialization_context()
 
-    components = ctx.serialize(pd_obj).to_components()
-    deserialized = ctx.deserialize_components(components)
+    with pytest.warns(DeprecationWarning):
+        components = ctx.serialize(pd_obj).to_components()
+    with pytest.warns(DeprecationWarning):
+        deserialized = ctx.deserialize_components(components)
 
     if isinstance(pd_obj, pd.DataFrame):
         tm.assert_frame_equal(pd_obj, deserialized)
diff --git a/python/pyarrow/tests/test_serialization.py b/python/pyarrow/tests/test_serialization.py
index f1e0cf42563..0a0338fab52 100644
--- a/python/pyarrow/tests/test_serialization.py
+++ b/python/pyarrow/tests/test_serialization.py
@@ -52,6 +52,9 @@
     sparse = None
 
 
+pytestmark = pytest.mark.filterwarnings("ignore:'pyarrow:DeprecationWarning")
+
+
 def assert_equal(obj1, obj2):
     if torch is not None and torch.is_tensor(obj1) and torch.is_tensor(obj2):
         if obj1.is_sparse:
@@ -233,7 +236,8 @@ class CustomError(Exception):
 
 
 def make_serialization_context():
-    context = pa.default_serialization_context()
+    with pytest.warns(DeprecationWarning):
+        context = pa.default_serialization_context()
 
     context.register_type(Foo, "Foo")
     context.register_type(Bar, "Bar")

From 7f2ce90f88faa91c00c285b43d063db366c7e223 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Wed, 30 Sep 2020 17:02:07 +0200
Subject: [PATCH 2/6] more deprecations + tests + basic docs

---
 docs/source/python/api/ipc.rst                |  7 +++
 docs/source/python/ipc.rst                    | 22 +++++---
 python/pyarrow/__init__.py                    | 24 ++++++++-
 python/pyarrow/serialization.pxi              |  6 +--
 python/pyarrow/serialization.py               | 19 ++++++-
 .../tests/test_serialization_deprecated.py    | 51 +++++++++++++++++++
 6 files changed, 116 insertions(+), 13 deletions(-)
 create mode 100644 python/pyarrow/tests/test_serialization_deprecated.py

diff --git a/docs/source/python/api/ipc.rst b/docs/source/python/api/ipc.rst
index f4c0a17dba9..cc3ccfe40bc 100644
--- a/docs/source/python/api/ipc.rst
+++ b/docs/source/python/api/ipc.rst
@@ -48,6 +48,13 @@ Inter-Process Communication
 Serialization
 -------------
 
+.. warning::
+
+   The serialization functionality is deprecated in pyarrow 2.0, and will
+   be removed in a future version. Use the standard library ``pickle`` or
+   the IPC functionality of pyarrow (see :ref:`ipc`).
+
+
 .. autosummary::
    :toctree: ../generated/
 
diff --git a/docs/source/python/ipc.rst b/docs/source/python/ipc.rst
index b7a032d1342..5eeedbdae89 100644
--- a/docs/source/python/ipc.rst
+++ b/docs/source/python/ipc.rst
@@ -157,17 +157,25 @@ DataFrame output:
 Arbitrary Object Serialization
 ------------------------------
 
+.. warning::
+
+   The custom serialization functionality is deprecated in pyarrow 2.0, and
+   will be removed in a future version.
+
+   While the serialization functions in this section utilize the Arrow stream
+   protocol internally, they do not produce data that is compatible with the
+   above ``ipc.open_file`` and ``ipc.open_stream`` functions.
+
+   For arbitrary objects, you can use the standard library ``pickle``
+   functionality instead. For pyarrow objects, you can use the IPC
+   serialization format through the ``pyarrow.ipc`` module, as explained
+   above.
+
 In ``pyarrow`` we are able to serialize and deserialize many kinds of Python
 objects. While not a complete replacement for the ``pickle`` module, these
 functions can be significantly faster, particular when dealing with collections
 of NumPy arrays.
 
-.. warning::
-
-   While the functions in this section utilize the Arrow stream protocol
-   internally, they do not produce data that is compatible with the above
-   ``ipc.open_file`` and ``ipc.open_stream`` functions.
-
 As an example, consider a dictionary containing NumPy arrays:
 
 .. ipython:: python
@@ -324,7 +332,7 @@ An object can be reconstructed from its component-based representation using
 ``SerializationContext`` objects.
 
 Serializing pandas Objects
---------------------------
+~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 The default serialization context has optimized handling of pandas
 objects like ``DataFrame`` and ``Series``. Combined with component-based
diff --git a/python/pyarrow/__init__.py b/python/pyarrow/__init__.py
index 9f544a12184..722f8e9527f 100644
--- a/python/pyarrow/__init__.py
+++ b/python/pyarrow/__init__.py
@@ -187,7 +187,6 @@ def show_versions():
 from pyarrow.lib import (deserialize_from, deserialize,
                          deserialize_components,
                          serialize, serialize_to, read_serialized,
-                         SerializedPyObject, SerializationContext,
                          SerializationCallbackError,
                          DeserializationCallbackError)
 
@@ -203,16 +202,26 @@ def show_versions():
 import pyarrow.types as types
 
 
-# deprecated filesystems
+# deprecated top-level access
+
 
 from pyarrow.filesystem import FileSystem as _FileSystem, LocalFileSystem as _LocalFileSystem
 from pyarrow.hdfs import HadoopFileSystem as _HadoopFileSystem
 
+from pyarrow.lib import SerializationContext as _SerializationContext
+from pyarrow.lib import SerializedPyObject as _SerializedPyObject
+
+
 _localfs = _LocalFileSystem._get_instance()
 
 
 _msg = "pyarrow.{0} is deprecated as of 2.0.0, please use pyarrow.fs.{1} instead."
 
+_serialization_msg = (
+    "'pyarrow.{0}' is deprecated and will be removed in a future version. "
+    "Use pickle or the pyarrow IPC functionality instead."
+)
+
 _deprecated = {
     "localfs": (_localfs, "LocalFileSystem"),
     "FileSystem": (_FileSystem, "FileSystem"),
@@ -220,6 +229,11 @@ def show_versions():
     "HadoopFileSystem": (_HadoopFileSystem, "HadoopFileSystem"),
 }
 
+_serialization_deprecatd = {
+    "SerializationContext": _SerializationContext,
+    "SerializedPyObject": _SerializedPyObject,
+}
+
 if _sys.version_info >= (3, 7):
     def __getattr__(name):
         if name in _deprecated:
@@ -227,6 +241,10 @@ def __getattr__(name):
             _warnings.warn(_msg.format(name, new_name),
                            DeprecationWarning, stacklevel=2)
             return obj
+        elif name in _serialization_deprecatd:
+            _warnings.warn(_msg.format(name),
+                           DeprecationWarning, stacklevel=2)
+            return _serialization_deprecatd[name]
 
         raise AttributeError(
             "module 'pyarrow' has no attribute '{0}'".format(name)
@@ -236,6 +254,8 @@ def __getattr__(name):
     FileSystem = _FileSystem
     LocalFileSystem = _LocalFileSystem
     HadoopFileSystem = _HadoopFileSystem
+    SerializationContext = _SerializationContext
+    SerializedPyObject = _SerializedPyObject
 
 
 # Entry point for starting the plasma store
diff --git a/python/pyarrow/serialization.pxi b/python/pyarrow/serialization.pxi
index 10c7eef74cc..9feada3c0e2 100644
--- a/python/pyarrow/serialization.pxi
+++ b/python/pyarrow/serialization.pxi
@@ -45,7 +45,6 @@ class DeserializationCallbackError(ArrowSerializationError):
         self.type_id = type_id
 
 
-# TODO deprecate accessing this class top-level
 cdef class SerializationContext(_Weakrefable):
     cdef:
         object type_to_type_id
@@ -227,9 +226,10 @@ _default_context_initialized = False
 
 def _get_default_context():
     global _default_context_initialized
-    from pyarrow.serialization import register_default_serialization_handlers
+    from pyarrow.serialization import _register_default_serialization_handlers
     if not _default_context_initialized:
-        register_default_serialization_handlers(_default_serialization_context)
+        _register_default_serialization_handlers(
+            _default_serialization_context)
         _default_context_initialized = True
     return _default_serialization_context
 
diff --git a/python/pyarrow/serialization.py b/python/pyarrow/serialization.py
index 408ae7c7185..8acb7abfe7f 100644
--- a/python/pyarrow/serialization.py
+++ b/python/pyarrow/serialization.py
@@ -263,6 +263,13 @@ def register_torch_serialization_handlers(serialization_context):
     # ----------------------------------------------------------------------
     # Set up serialization for pytorch tensors
 
+    warnings.warn(
+        "'pyarrow.register_torch_serialization_handlers' is deprecated and "
+        "will be removed in a future version. Use pickle or the pyarrow IPC "
+        "functionality instead.",
+        DeprecationWarning, stacklevel=2
+    )
+
     try:
         import torch
 
@@ -433,7 +440,7 @@ def _deserialize_pydata_sparse(data):
         pass
 
 
-def register_default_serialization_handlers(serialization_context):
+def _register_default_serialization_handlers(serialization_context):
 
     # ----------------------------------------------------------------------
     # Set up serialization for primitive datatypes
@@ -483,6 +490,16 @@ def register_default_serialization_handlers(serialization_context):
     _register_pydata_sparse_handlers(serialization_context)
 
 
+def register_default_serialization_handlers(serialization_context):
+    warnings.warn(
+        "'pyarrow.register_default_serialization_handlers' is deprecated and "
+        "will be removed in a future version. Use pickle or the pyarrow IPC "
+        "functionality instead.",
+        DeprecationWarning, stacklevel=2
+    )
+    _register_default_serialization_handlers(serialization_context)
+
+
 def default_serialization_context():
     warnings.warn(
         "'pyarrow.default_serialization_context' is deprecated and will be "
diff --git a/python/pyarrow/tests/test_serialization_deprecated.py b/python/pyarrow/tests/test_serialization_deprecated.py
new file mode 100644
index 00000000000..d38c1c7cd24
--- /dev/null
+++ b/python/pyarrow/tests/test_serialization_deprecated.py
@@ -0,0 +1,51 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+
+import pytest
+
+import pyarrow as pa
+
+
+def test_serialization_deprecated():
+
+    with pytest.warns(DeprecationWarning):
+        ser = pa.serialize(1)
+
+    with pytest.warns(DeprecationWarning):
+        pa.deserialize(ser.to_buffer())
+
+    f = pa.BufferOutputStream()
+    with pytest.warns(DeprecationWarning):
+        pa.serialize_to(12, f)
+
+    buf = f.getvalue()
+    f = pa.BufferReader(buf)
+    with pytest.warns(DeprecationWarning):
+        pa.read_serialized(f).deserialize()
+
+    with pytest.warns(DeprecationWarning):
+        pa.default_serialization_context()
+
+    with pytest.warns(DeprecationWarning):
+        pa.SerializedPyObject()
+
+    with pytest.warns(DeprecationWarning):
+        context = pa.SerializationContext()
+
+    with pytest.warns(DeprecationWarning):
+        pa.register_default_serialization_handlers(context)

From 67a0f67eb44f30ee2e548324ca22e29ec35604d6 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Wed, 7 Oct 2020 10:41:08 +0200
Subject: [PATCH 3/6] fixup tests for older python

---
 python/pyarrow/serialization.py                      |  2 +-
 .../pyarrow/tests/test_serialization_deprecated.py   | 12 +++++++++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/python/pyarrow/serialization.py b/python/pyarrow/serialization.py
index 8acb7abfe7f..8670b91cabb 100644
--- a/python/pyarrow/serialization.py
+++ b/python/pyarrow/serialization.py
@@ -508,5 +508,5 @@ def default_serialization_context():
         DeprecationWarning, stacklevel=2
     )
     context = SerializationContext()
-    register_default_serialization_handlers(context)
+    _register_default_serialization_handlers(context)
     return context
diff --git a/python/pyarrow/tests/test_serialization_deprecated.py b/python/pyarrow/tests/test_serialization_deprecated.py
index d38c1c7cd24..8c48f513d86 100644
--- a/python/pyarrow/tests/test_serialization_deprecated.py
+++ b/python/pyarrow/tests/test_serialization_deprecated.py
@@ -15,6 +15,7 @@
 # specific language governing permissions and limitations
 # under the License.
 
+import sys
 
 import pytest
 
@@ -41,11 +42,16 @@ def test_serialization_deprecated():
     with pytest.warns(DeprecationWarning):
         pa.default_serialization_context()
 
+    context = pa.lib.SerializationContext()
     with pytest.warns(DeprecationWarning):
-        pa.SerializedPyObject()
+        pa.register_default_serialization_handlers(context)
+
 
+@pytest.mark.skipif(sys.version_info < (3, 7),
+                    reason="getattr needs Python 3.7")
+def test_serialization_deprecated_toplevel():
     with pytest.warns(DeprecationWarning):
-        context = pa.SerializationContext()
+        pa.SerializedPyObject()
 
     with pytest.warns(DeprecationWarning):
-        pa.register_default_serialization_handlers(context)
+        pa.SerializationContext()

From 17b0b19a1288498b40f7d07762ef1f76c902e463 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Wed, 7 Oct 2020 16:46:35 +0200
Subject: [PATCH 4/6] use helper function to deduplicate warnings

---
 python/pyarrow/serialization.pxi           | 45 +++++++---------------
 python/pyarrow/serialization.py            | 30 ++++++---------
 python/pyarrow/tests/test_serialization.py |  2 +
 3 files changed, 27 insertions(+), 50 deletions(-)

diff --git a/python/pyarrow/serialization.pxi b/python/pyarrow/serialization.pxi
index 9feada3c0e2..b8d7df54b15 100644
--- a/python/pyarrow/serialization.pxi
+++ b/python/pyarrow/serialization.pxi
@@ -20,6 +20,14 @@ from cpython.ref cimport PyObject
 import warnings
 
 
+def _deprecate_serialization(name):
+    msg = (
+        "'pyarrow.{}' is deprecated as of 2.0.0 and will be removed in a "
+        "future version. Use pickle or the pyarrow IPC functionality instead."
+    ).format(name)
+    warnings.warn(msg, DeprecationWarning, stacklevel=3)
+
+
 def is_named_tuple(cls):
     """
     Return True if cls is a namedtuple and False otherwise.
@@ -372,11 +380,7 @@ def serialize(object value, SerializationContext context=None):
     serialized : SerializedPyObject
 
     """
-    warnings.warn(
-        "'pyarrow.serialize' is deprecated and will be removed in a future "
-        "version. Use pickle or the pyarrow IPC functionality instead.",
-        DeprecationWarning, stacklevel=2
-    )
+    _deprecate_serialization("serialize")
     return _serialize(value, context)
 
 
@@ -406,11 +410,7 @@ def serialize_to(object value, sink, SerializationContext context=None):
         Custom serialization and deserialization context, uses a default
         context with some standard type handlers if not specified.
     """
-    warnings.warn(
-        "'pyarrow.serialize_to' is deprecated and will be removed in a future "
-        "version. Use pickle or the pyarrow IPC functionality instead.",
-        DeprecationWarning, stacklevel=2
-    )
+    _deprecate_serialization("serialize_to")
     serialized = _serialize(value, context)
     serialized.write_to(sink)
 
@@ -431,11 +431,7 @@ def read_serialized(source, base=None):
     -------
     serialized : the serialized data
     """
-    warnings.warn(
-        "'pyarrow.read_serialized' is deprecated and will be removed in a "
-        "future version. Use pickle or the pyarrow IPC functionality instead.",
-        DeprecationWarning, stacklevel=2
-    )
+    _deprecate_serialization("read_serialized")
     return _read_serialized(source, base=base)
 
 
@@ -473,11 +469,7 @@ def deserialize_from(source, object base, SerializationContext context=None):
     object
         Python object for the deserialized sequence.
     """
-    warnings.warn(
-        "'pyarrow.deserialize_from' is deprecated and will be removed in a "
-        "future version. Use pickle or the pyarrow IPC functionality instead.",
-        DeprecationWarning, stacklevel=2
-    )
+    _deprecate_serialization("deserialize_from")
     serialized = _read_serialized(source, base=base)
     return serialized.deserialize(context)
 
@@ -496,12 +488,7 @@ def deserialize_components(components, SerializationContext context=None):
     -------
     object : the Python object that was originally serialized
     """
-    warnings.warn(
-        "'pyarrow.deserialize_components' is deprecated and will be removed "
-        "in a future version. Use pickle or the pyarrow IPC functionality "
-        "instead.",
-        DeprecationWarning, stacklevel=2
-    )
+    _deprecate_serialization("deserialize_components")
     serialized = SerializedPyObject.from_components(components)
     return serialized.deserialize(context)
 
@@ -524,11 +511,7 @@ def deserialize(obj, SerializationContext context=None):
     -------
     deserialized : object
     """
-    warnings.warn(
-        "'pyarrow.deserialize' is deprecated and will be removed in a future "
-        "version. Use pickle or the pyarrow IPC functionality instead.",
-        DeprecationWarning, stacklevel=2
-    )
+    _deprecate_serialization("deserialize")
     return _deserialize(obj, context=context)
 
 
diff --git a/python/pyarrow/serialization.py b/python/pyarrow/serialization.py
index 8670b91cabb..5e8ea697ccb 100644
--- a/python/pyarrow/serialization.py
+++ b/python/pyarrow/serialization.py
@@ -76,6 +76,14 @@ def descr_to_dtype(descr):
                          'offsets': offsets, 'itemsize': offset})
 
 
+def _deprecate_serialization(name):
+    msg = (
+        "'pyarrow.{}' is deprecated as of 2.0.0 and will be removed in a "
+        "future version. Use pickle or the pyarrow IPC functionality instead."
+    ).format(name)
+    warnings.warn(msg, DeprecationWarning, stacklevel=3)
+
+
 # ----------------------------------------------------------------------
 # Set up serialization for numpy with dtype object (primitive types are
 # handled efficiently with Arrow's Tensor facilities, see
@@ -262,13 +270,7 @@ def _deserialize_pandas_series(data):
 def register_torch_serialization_handlers(serialization_context):
     # ----------------------------------------------------------------------
     # Set up serialization for pytorch tensors
-
-    warnings.warn(
-        "'pyarrow.register_torch_serialization_handlers' is deprecated and "
-        "will be removed in a future version. Use pickle or the pyarrow IPC "
-        "functionality instead.",
-        DeprecationWarning, stacklevel=2
-    )
+    _deprecate_serialization("register_torch_serialization_handlers")
 
     try:
         import torch
@@ -491,22 +493,12 @@ def _register_default_serialization_handlers(serialization_context):
 
 
 def register_default_serialization_handlers(serialization_context):
-    warnings.warn(
-        "'pyarrow.register_default_serialization_handlers' is deprecated and "
-        "will be removed in a future version. Use pickle or the pyarrow IPC "
-        "functionality instead.",
-        DeprecationWarning, stacklevel=2
-    )
+    _deprecate_serialization("register_default_serialization_handlers")
     _register_default_serialization_handlers(serialization_context)
 
 
 def default_serialization_context():
-    warnings.warn(
-        "'pyarrow.default_serialization_context' is deprecated and will be "
-        "removed in a future version. Use pickle or the pyarrow IPC "
-        "functionality instead.",
-        DeprecationWarning, stacklevel=2
-    )
+    _deprecate_serialization("default_serialization_context")
     context = SerializationContext()
     _register_default_serialization_handlers(context)
     return context
diff --git a/python/pyarrow/tests/test_serialization.py b/python/pyarrow/tests/test_serialization.py
index 0a0338fab52..456f42c92fa 100644
--- a/python/pyarrow/tests/test_serialization.py
+++ b/python/pyarrow/tests/test_serialization.py
@@ -52,6 +52,8 @@
     sparse = None
 
 
+# ignore all serialization deprecation warnings in this file, we test that the
+# warnings are actually raised in test_serialization_deprecated.py
 pytestmark = pytest.mark.filterwarnings("ignore:'pyarrow:DeprecationWarning")
 
 

From e8c4941cfe375f14273ffd45841a969535cb4b58 Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Fri, 9 Oct 2020 10:14:30 +0200
Subject: [PATCH 5/6] fixup

---
 python/pyarrow/__init__.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/python/pyarrow/__init__.py b/python/pyarrow/__init__.py
index 722f8e9527f..ffc0be402d3 100644
--- a/python/pyarrow/__init__.py
+++ b/python/pyarrow/__init__.py
@@ -242,7 +242,7 @@ def __getattr__(name):
                            DeprecationWarning, stacklevel=2)
             return obj
         elif name in _serialization_deprecatd:
-            _warnings.warn(_msg.format(name),
+            _warnings.warn(_serialization_msg.format(name),
                            DeprecationWarning, stacklevel=2)
             return _serialization_deprecatd[name]
 

From 17837644bd1e38b16e98c9f15ab64353d6fff13f Mon Sep 17 00:00:00 2001
From: Joris Van den Bossche <jorisvandenbossche@gmail.com>
Date: Fri, 9 Oct 2020 12:06:44 +0200
Subject: [PATCH 6/6] lint

---
 python/pyarrow/__init__.py                            | 7 +++++--
 python/pyarrow/tests/test_serialization_deprecated.py | 1 -
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/python/pyarrow/__init__.py b/python/pyarrow/__init__.py
index ffc0be402d3..1dd209a66fc 100644
--- a/python/pyarrow/__init__.py
+++ b/python/pyarrow/__init__.py
@@ -205,7 +205,8 @@ def show_versions():
 # deprecated top-level access
 
 
-from pyarrow.filesystem import FileSystem as _FileSystem, LocalFileSystem as _LocalFileSystem
+from pyarrow.filesystem import FileSystem as _FileSystem
+from pyarrow.filesystem import LocalFileSystem as _LocalFileSystem
 from pyarrow.hdfs import HadoopFileSystem as _HadoopFileSystem
 
 from pyarrow.lib import SerializationContext as _SerializationContext
@@ -215,7 +216,9 @@ def show_versions():
 _localfs = _LocalFileSystem._get_instance()
 
 
-_msg = "pyarrow.{0} is deprecated as of 2.0.0, please use pyarrow.fs.{1} instead."
+_msg = (
+    "pyarrow.{0} is deprecated as of 2.0.0, please use pyarrow.fs.{1} instead."
+)
 
 _serialization_msg = (
     "'pyarrow.{0}' is deprecated and will be removed in a future version. "
diff --git a/python/pyarrow/tests/test_serialization_deprecated.py b/python/pyarrow/tests/test_serialization_deprecated.py
index 8c48f513d86..f818d56b4d3 100644
--- a/python/pyarrow/tests/test_serialization_deprecated.py
+++ b/python/pyarrow/tests/test_serialization_deprecated.py
@@ -23,7 +23,6 @@
 
 
 def test_serialization_deprecated():
-
     with pytest.warns(DeprecationWarning):
         ser = pa.serialize(1)