Fix copying generic instances in Python 3 (#502)

Fixes #498 (on both Python 2 and 3)

Author: ilevkivskyi

python2/test_typing.py

@@ -1024,6 +1024,30 @@ class Node(Generic[T]): pass
             self.assertEqual(t, deepcopy(t))
             self.assertEqual(t, copy(t))
 
+    def test_copy_generic_instances(self):
+        T = TypeVar('T')
+        class C(Generic[T]):
+            def __init__(self, attr):
+                self.attr = attr
+
+        c = C(42)
+        self.assertEqual(copy(c).attr, 42)
+        self.assertEqual(deepcopy(c).attr, 42)
+        self.assertIsNot(copy(c), c)
+        self.assertIsNot(deepcopy(c), c)
+        c.attr = 1
+        self.assertEqual(copy(c).attr, 1)
+        self.assertEqual(deepcopy(c).attr, 1)
+        ci = C[int](42)
+        self.assertEqual(copy(ci).attr, 42)
+        self.assertEqual(deepcopy(ci).attr, 42)
+        self.assertIsNot(copy(ci), ci)
+        self.assertIsNot(deepcopy(ci), ci)
+        ci.attr = 1
+        self.assertEqual(copy(ci).attr, 1)
+        self.assertEqual(deepcopy(ci).attr, 1)
+        self.assertEqual(ci.__orig_class__, C[int])
+
     def test_weakref_all(self):
         T = TypeVar('T')
         things = [Any, Union[T, int], Callable[..., T], Tuple[Any, Any],

python2/typing.py

@@ -7,6 +7,7 @@
 import re as stdlib_re  # Avoid confusion with the re we export.
 import sys
 import types
+import copy
 try:
     import collections.abc as collections_abc
 except ImportError:
@@ -1253,11 +1254,6 @@ def __instancecheck__(self, instance):
             return issubclass(instance.__class__, self)
         return False
 
-    def __copy__(self):
-        return self.__class__(self.__name__, self.__bases__, dict(self.__dict__),
-                              self.__parameters__, self.__args__, self.__origin__,
-                              self.__extra__, self.__orig_bases__)
-
     def __setattr__(self, attr, value):
         # We consider all the subscripted genrics as proxies for original class
         if (
@@ -1269,6 +1265,16 @@ def __setattr__(self, attr, value):
             super(GenericMeta, self._gorg).__setattr__(attr, value)
 
 
+def _copy_generic(self):
+    """Hack to work around https://bugs.python.org/issue11480 on Python 2"""
+    return self.__class__(self.__name__, self.__bases__, dict(self.__dict__),
+                          self.__parameters__, self.__args__, self.__origin__,
+                          self.__extra__, self.__orig_bases__)
+
+
+copy._copy_dispatch[GenericMeta] = _copy_generic
+
+
 # Prevent checks for Generic to crash when defining Generic.
 Generic = None
 
@@ -1365,6 +1371,9 @@ def __subclasscheck__(self, cls):
                         "with issubclass().")
 
 
+copy._copy_dispatch[TupleMeta] = _copy_generic
+
+
 class Tuple(tuple):
     """Tuple type; Tuple[X, Y] is the cross-product type of X and Y.
 
@@ -1443,6 +1452,9 @@ def __getitem_inner__(self, parameters):
         return super(CallableMeta, self).__getitem__(parameters)
 
 
+copy._copy_dispatch[CallableMeta] = _copy_generic
+
+
 class Callable(object):
     """Callable type; Callable[[int], str] is a function of (int) -> str.
 

src/test_typing.py

@@ -1080,6 +1080,30 @@ class Node(Generic[T]): ...
                 self.assertTrue(t is copy(t))
                 self.assertTrue(t is deepcopy(t))
 
+    def test_copy_generic_instances(self):
+        T = TypeVar('T')
+        class C(Generic[T]):
+            def __init__(self, attr: T) -> None:
+                self.attr = attr
+
+        c = C(42)
+        self.assertEqual(copy(c).attr, 42)
+        self.assertEqual(deepcopy(c).attr, 42)
+        self.assertIsNot(copy(c), c)
+        self.assertIsNot(deepcopy(c), c)
+        c.attr = 1
+        self.assertEqual(copy(c).attr, 1)
+        self.assertEqual(deepcopy(c).attr, 1)
+        ci = C[int](42)
+        self.assertEqual(copy(ci).attr, 42)
+        self.assertEqual(deepcopy(ci).attr, 42)
+        self.assertIsNot(copy(ci), ci)
+        self.assertIsNot(deepcopy(ci), ci)
+        ci.attr = 1
+        self.assertEqual(copy(ci).attr, 1)
+        self.assertEqual(deepcopy(ci).attr, 1)
+        self.assertEqual(ci.__orig_class__, C[int])
+
     def test_weakref_all(self):
         T = TypeVar('T')
         things = [Any, Union[T, int], Callable[..., T], Tuple[Any, Any],

src/typing.py

@@ -1160,12 +1160,6 @@ def __instancecheck__(self, instance):
         # classes are supposed to be rare anyways.
         return issubclass(instance.__class__, self)
 
-    def __copy__(self):
-        return self.__class__(self.__name__, self.__bases__,
-                              _no_slots_copy(self.__dict__),
-                              self.__parameters__, self.__args__, self.__origin__,
-                              self.__extra__, self.__orig_bases__)
-
     def __setattr__(self, attr, value):
         # We consider all the subscripted generics as proxies for original class
         if (