Issue #28790: Fix error when using Generic and __slots__ (Ivan L)

1 files changed, 15 insertions, 3 deletions

diff --git a/Lib/typing.py b/Lib/typing.py
index 1a943aca20..34845b747a 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -870,6 +870,17 @@ def _make_subclasshook(cls):
     return __extrahook__
 
 
+def _no_slots_copy(dct):
+    """Internal helper: copy class __dict__ and clean slots class variables.
+    (They will be re-created if necessary by normal class machinery.)
+    """
+    dict_copy = dict(dct)
+    if '__slots__' in dict_copy:
+        for slot in dict_copy['__slots__']:
+            dict_copy.pop(slot, None)
+    return dict_copy
+
+
 class GenericMeta(TypingMeta, abc.ABCMeta):
     """Metaclass for generic types."""
 
@@ -967,7 +978,7 @@ class GenericMeta(TypingMeta, abc.ABCMeta):
             return self
         return self.__class__(self.__name__,
                               self.__bases__,
-                              dict(self.__dict__),
+                              _no_slots_copy(self.__dict__),
                               tvars=_type_vars(ev_args) if ev_args else None,
                               args=ev_args,
                               origin=ev_origin,
@@ -1043,7 +1054,7 @@ class GenericMeta(TypingMeta, abc.ABCMeta):
             args = params
         return self.__class__(self.__name__,
                               self.__bases__,
-                              dict(self.__dict__),
+                              _no_slots_copy(self.__dict__),
                               tvars=tvars,
                               args=args,
                               origin=self,
@@ -1059,7 +1070,8 @@ class GenericMeta(TypingMeta, abc.ABCMeta):
         return issubclass(instance.__class__, self)
 
     def __copy__(self):
-        return self.__class__(self.__name__, self.__bases__, dict(self.__dict__),
+        return self.__class__(self.__name__, self.__bases__,
+                              _no_slots_copy(self.__dict__),
                               self.__parameters__, self.__args__, self.__origin__,
                               self.__extra__, self.__orig_bases__)