Pickling of generic annotations/types in 3.5+

.github/workflows/testing.yml

@@ -61,6 +61,10 @@ jobs:
         python -m pip install -r dev-requirements.txt
         python ci/install_coverage_subprocess_pth.py
         export
+    - name: Install optional typing_extensions in Python 3.6
+      shell: bash
+      run: python -m pip install typing-extensions
+      if: matrix.python_version == '3.6'
     - name: Display Python version
       shell: bash
       run: python -c "import sys; print(sys.version)"

CHANGES.md

@@ -15,6 +15,10 @@
   instances on Python 3.7+
   ([PR #351](https://github.com/cloudpipe/cloudpickle/pull/351))
 
+- Add support for pickling dynamic classes subclassing `typing.Generic`
+  instances on Python 3.5+
+  ([PR #318](https://github.com/cloudpipe/cloudpickle/pull/318))
+
 1.3.0
 =====
 

cloudpickle/cloudpickle.py

@@ -61,11 +61,18 @@
 import typing
 from enum import Enum
 
+from typing import Generic, Union, Tuple, Callable, ClassVar
 from pickle import _Pickler as Pickler
 from pickle import _getattribute
 from io import BytesIO
 from importlib._bootstrap import _find_spec
 
+try:  # pragma: no branch
+    import typing_extensions as _typing_extensions
+    from typing_extensions import Literal, Final
+except ImportError:
+    _typing_extensions = Literal = Final = None
+
 
 # cloudpickle is meant for inter process communication: we expect all
 # communicating processes to run the same Python version hence we favor
@@ -117,7 +124,18 @@ def _whichmodule(obj, name):
     - Errors arising during module introspection are ignored, as those errors
       are considered unwanted side effects.
     """
-    module_name = _get_module_attr(obj)
+    if sys.version_info[:2] < (3, 7) and isinstance(obj, typing.TypeVar):  # pragma: no branch  # noqa
+        # Workaround bug in old Python versions: prior to Python 3.7,
+        # T.__module__ would always be set to "typing" even when the TypeVar T
+        # would be defined in a different module.
+        #
+        # For such older Python versions, we ignore the __module__ attribute of
+        # TypeVar instances and instead exhaustively lookup those instances in
+        # all currently imported modules.
+        module_name = None
+    else:
+        module_name = getattr(obj, '__module__', None)
+
     if module_name is not None:
         return module_name
     # Protect the iteration by using a copy of sys.modules against dynamic
@@ -140,23 +158,6 @@ def _whichmodule(obj, name):
     return None
 
 
-if sys.version_info[:2] < (3, 7):  # pragma: no branch
-    # Workaround bug in old Python versions: prior to Python 3.7, T.__module__
-    # would always be set to "typing" even when the TypeVar T would be defined
-    # in a different module.
-    #
-    # For such older Python versions, we ignore the __module__ attribute of
-    # TypeVar instances and instead exhaustively lookup those instances in all
-    # currently imported modules via the _whichmodule function.
-    def _get_module_attr(obj):
-        if isinstance(obj, typing.TypeVar):
-            return None
-        return getattr(obj, '__module__', None)
-else:
-    def _get_module_attr(obj):
-        return getattr(obj, '__module__', None)
-
-
 def _is_importable_by_name(obj, name=None):
     """Determine if obj can be pickled as attribute of a file-backed module"""
     return _lookup_module_and_qualname(obj, name=name) is not None
@@ -423,6 +424,18 @@ def _extract_class_dict(cls):
     return clsdict
 
 
+if sys.version_info[:2] < (3, 7):  # pragma: no branch
+    def _is_parametrized_type_hint(obj):
+        # This is very cheap but might generate false positives.
+        origin = getattr(obj, '__origin__', None)  # typing Constructs
+        values = getattr(obj, '__values__', None)  # typing_extensions.Literal
+        type_ = getattr(obj, '__type__', None)     # typing_extensions.Final
+        return origin is not None or values is not None or type_ is not None
+
+    def _create_parametrized_type_hint(origin, args):
+        return origin[args]
+
+
 class CloudPickler(Pickler):
 
     dispatch = Pickler.dispatch.copy()
@@ -611,11 +624,6 @@ def save_dynamic_class(self, obj):
         if isinstance(__dict__, property):
             type_kwargs['__dict__'] = __dict__
 
-        if sys.version_info < (3, 7):
-            # Although annotations were added in Python 3.4, It is not possible
-            # to properly pickle them until Python 3.7. (See #193)
-            clsdict.pop('__annotations__', None)
-
         save = self.save
         write = self.write
 
@@ -715,9 +723,7 @@ def save_function_tuple(self, func):
             'doc': func.__doc__,
             '_cloudpickle_submodules': submodules
         }
-        if hasattr(func, '__annotations__') and sys.version_info >= (3, 7):
-            # Although annotations were added in Python3.4, It is not possible
-            # to properly pickle them until Python3.7. (See #193)
+        if hasattr(func, '__annotations__'):
             state['annotations'] = func.__annotations__
         if hasattr(func, '__qualname__'):
             state['qualname'] = func.__qualname__
@@ -800,6 +806,14 @@ def save_global(self, obj, name=None, pack=struct.pack):
         elif obj in _BUILTIN_TYPE_NAMES:
             return self.save_reduce(
                 _builtin_type, (_BUILTIN_TYPE_NAMES[obj],), obj=obj)
+
+        if sys.version_info[:2] < (3, 7) and _is_parametrized_type_hint(obj):  # noqa  # pragma: no branch
+            # Parametrized typing constructs in Python < 3.7 are not compatible
+            # with type checks and ``isinstance`` semantics. For this reason,
+            # it is easier to detect them using a duck-typing-based check
+            # (``_is_parametrized_type_hint``) than to populate the Pickler's
+            # dispatch with type-specific savers.
+            self._save_parametrized_type_hint(obj)
         elif name is not None:
             Pickler.save_global(self, obj, name=name)
         elif not _is_importable_by_name(obj, name=name):
@@ -941,6 +955,31 @@ def inject_addons(self):
         """Plug in system. Register additional pickling functions if modules already loaded"""
         pass
 
+    if sys.version_info < (3, 7):  # pragma: no branch
+        def _save_parametrized_type_hint(self, obj):
+            # The distorted type check sematic for typing construct becomes:
+            # ``type(obj) is type(TypeHint)``, which means "obj is a
+            # parametrized TypeHint"
+            if type(obj) is type(Literal):  # pragma: no branch
+                initargs = (Literal, obj.__values__)
+            elif type(obj) is type(Final):  # pragma: no branch
+                initargs = (Final, obj.__type__)
+            elif type(obj) is type(ClassVar):
+                initargs = (ClassVar, obj.__type__)
+            elif type(obj) in [type(Union), type(Tuple), type(Generic)]:
+                initargs = (obj.__origin__, obj.__args__)
+            elif type(obj) is type(Callable):
+                args = obj.__args__
+                if args[0] is Ellipsis:
+                    initargs = (obj.__origin__, args)
+                else:
+                    initargs = (obj.__origin__, (list(args[:-1]), args[-1]))
+            else:  # pragma: no cover
+                raise pickle.PicklingError(
+                    "Cloudpickle Error: Unknown type {}".format(type(obj))
+                )
+            self.save_reduce(_create_parametrized_type_hint, initargs, obj=obj)
+
 
 # Tornado support
 

tests/cloudpickle_test.py

@@ -1787,9 +1787,6 @@ def g():
 
         self.assertEqual(f2.__doc__, f.__doc__)
 
-    @unittest.skipIf(sys.version_info < (3, 7),
-                     "Pickling type annotations isn't supported for py36 and "
-                     "below.")
     def test_wraps_preserves_function_annotations(self):
         def f(x):
             pass
@@ -1804,79 +1801,7 @@ def g(x):
 
         self.assertEqual(f2.__annotations__, f.__annotations__)
 
-    @unittest.skipIf(sys.version_info >= (3, 7),
-                     "pickling annotations is supported starting Python 3.7")
-    def test_function_annotations_silent_dropping(self):
-        # Because of limitations of typing module, cloudpickle does not pickle
-        # the type annotations of a dynamic function or class for Python < 3.7
-
-        class UnpicklableAnnotation:
-            # Mock Annotation metaclass that errors out loudly if we try to
-            # pickle one of its instances
-            def __reduce__(self):
-                raise Exception("not picklable")
-
-        unpickleable_annotation = UnpicklableAnnotation()
-
-        def f(a: unpickleable_annotation):
-            return a
-
-        with pytest.raises(Exception):
-            cloudpickle.dumps(f.__annotations__)
-
-        depickled_f = pickle_depickle(f, protocol=self.protocol)
-        assert depickled_f.__annotations__ == {}
-
-    @unittest.skipIf(sys.version_info >= (3, 7) or sys.version_info < (3, 6),
-                     "pickling annotations is supported starting Python 3.7")
-    def test_class_annotations_silent_dropping(self):
-        # Because of limitations of typing module, cloudpickle does not pickle
-        # the type annotations of a dynamic function or class for Python < 3.7
-
-        # Pickling and unpickling must be done in different processes when
-        # testing dynamic classes (see #313)
-
-        code = '''if 1:
-        import cloudpickle
-        import sys
-
-        class UnpicklableAnnotation:
-            # Mock Annotation metaclass that errors out loudly if we try to
-            # pickle one of its instances
-            def __reduce__(self):
-                raise Exception("not picklable")
-
-        unpickleable_annotation = UnpicklableAnnotation()
-
-        class A:
-            a: unpickleable_annotation
-
-        try:
-            cloudpickle.dumps(A.__annotations__)
-        except Exception:
-            pass
-        else:
-            raise AssertionError
-
-        sys.stdout.buffer.write(cloudpickle.dumps(A, protocol={protocol}))
-        '''
-        cmd = [sys.executable, '-c', code.format(protocol=self.protocol)]
-        proc = subprocess.Popen(
-                cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE
-        )
-        proc.wait()
-        out, err = proc.communicate()
-        assert proc.returncode == 0, err
-
-        depickled_a = pickle.loads(out)
-        assert not hasattr(depickled_a, "__annotations__")
-
-    @unittest.skipIf(sys.version_info < (3, 7),
-                     "Pickling type hints isn't supported for py36"
-                     " and below.")
     def test_type_hint(self):
-        # Try to pickle compound typing constructs. This would typically fail
-        # on Python < 3.7 (See #193)
         t = typing.Union[list, int]
         assert pickle_depickle(t) == t
 
@@ -2142,16 +2067,16 @@ def test_pickle_importable_typevar(self):
         from typing import AnyStr
         assert AnyStr is pickle_depickle(AnyStr, protocol=self.protocol)
 
-    @unittest.skipIf(sys.version_info < (3, 7),
-                     "Pickling generics not supported below py37")
     def test_generic_type(self):
         T = typing.TypeVar('T')
 
         class C(typing.Generic[T]):
             pass
 
         assert pickle_depickle(C, protocol=self.protocol) is C
-        assert pickle_depickle(C[int], protocol=self.protocol) is C[int]
+
+        # Identity is not part of the typing contract.
+        assert pickle_depickle(C[int], protocol=self.protocol) == C[int]
 
         with subprocess_worker(protocol=self.protocol) as worker:
 
@@ -2170,22 +2095,13 @@ def check_generic(generic, origin, type_value):
             assert check_generic(C[int], C, int) == "ok"
             assert worker.run(check_generic, C[int], C, int) == "ok"
 
-    @unittest.skipIf(sys.version_info < (3, 7),
-                     "Pickling type hints not supported below py37")
     def test_locally_defined_class_with_type_hints(self):
         with subprocess_worker(protocol=self.protocol) as worker:
             for type_ in _all_types_to_test():
-                # The type annotation syntax causes a SyntaxError on Python 3.5
-                code = textwrap.dedent("""\
                 class MyClass:
-                    attribute: type_
-
                     def method(self, arg: type_) -> type_:
                         return arg
-                """)
-                ns = {"type_": type_}
-                exec(code, ns)
-                MyClass = ns["MyClass"]
+                MyClass.__annotations__ = {'attribute': type_}
 
                 def check_annotations(obj, expected_type):
                     assert obj.__annotations__["attribute"] is expected_type
@@ -2197,6 +2113,34 @@ def check_annotations(obj, expected_type):
                 assert check_annotations(obj, type_) == "ok"
                 assert worker.run(check_annotations, obj, type_) == "ok"
 
+    def test_generic_extensions(self):
+        typing_extensions = pytest.importorskip('typing_extensions')
+
+        objs = [
+            typing_extensions.Literal,
+            typing_extensions.Final,
+            typing_extensions.Literal['a'],
+            typing_extensions.Final[int],
+        ]
+
+        for obj in objs:
+            _ = pickle_depickle(obj, protocol=self.protocol)
+
+    def test_class_annotations(self):
+        class C:
+            pass
+        C.__annotations__ = {'a': int}
+
+        C1 = pickle_depickle(C, protocol=self.protocol)
+        assert C1.__annotations__ == C.__annotations__
+
+    def test_function_annotations(self):
+        def f(a: int) -> str:
+            pass
+
+        f1 = pickle_depickle(f, protocol=self.protocol)
+        assert f1.__annotations__ == f.__annotations__
+
 
 class Protocol2CloudPickleTest(CloudPickleTest):