Add typing hints for twistedsupport.

testtools/twistedsupport/_deferred.py

@@ -2,8 +2,14 @@
 
 """Utilities for Deferreds."""
 
+from typing import List, TYPE_CHECKING
+
 from functools import partial
 
+if TYPE_CHECKING:
+    from twisted.python.failure import Failure
+    from twisted.internet.defer import Deferred
+
 from testtools.content import TracebackContent
 
 
@@ -29,8 +35,8 @@ def extract_result(deferred):
     code). In those cases, it is better to add callbacks and errbacks as
     needed.
     """
-    failures = []
-    successes = []
+    failures: List["Failure"] = []
+    successes: List["Deferred"] = []
     deferred.addCallbacks(successes.append, failures.append)
     if len(failures) == 1:
         failures[0].raiseException()
@@ -76,8 +82,8 @@ def on_deferred_result(deferred, on_success, on_failure, on_no_result):
     :return: Whatever is returned by the triggered callback.
     :rtype: ``T``
     """
-    successes = []
-    failures = []
+    successes: List["Deferred"] = []
+    failures: List["Failure"] = []
 
     def capture(value, values):
         values.append(value)

testtools/twistedsupport/_spinner.py

@@ -18,6 +18,7 @@
 
 from fixtures import Fixture
 import signal
+from typing import Union
 
 from ._deferreddebug import DebugTwisted
 
@@ -74,7 +75,7 @@ def trap_unhandled_errors(function, *args, **kwargs):
     # an instance doesn't work with Python 3 and viceversa overriding __del__
     # via inheritance doesn't work with Python 2. So we handle the two cases
     # differently. TODO: perhaps there's a way to have a single code path?
-    class DebugInfo(real_DebugInfo):
+    class DebugInfo(real_DebugInfo):  # type: ignore
 
         _runRealDel = True
 
@@ -86,11 +87,11 @@ def __del__(self):
             if self._runRealDel:
                 real_DebugInfo.__del__(self)
 
-    defer.DebugInfo = DebugInfo
+    defer.DebugInfo = DebugInfo  # type: ignore
     try:
         result = function(*args, **kwargs)
     finally:
-        defer.DebugInfo = real_DebugInfo
+        defer.DebugInfo = real_DebugInfo  # type: ignore
     errors = []
     for info in debug_infos:
         if info.failResult is not None:
@@ -153,6 +154,8 @@ class Spinner:
     # the ideal, and it actually works for many cases.
     _OBLIGATORY_REACTOR_ITERATIONS = 0
 
+    _failure: Union[Failure, object]
+
     def __init__(self, reactor, debug=False):
         """Construct a Spinner.
 
@@ -175,7 +178,7 @@ def _cancel_timeout(self):
 
     def _get_result(self):
         if self._failure is not self._UNSET:
-            self._failure.raiseException()
+            self._failure.raiseException()  # type: ignore
         if self._success is not self._UNSET:
             return self._success
         raise NoResultError()