Bring in protocol’s __init__ behaviour same like in python > 3.8 (#780)

typing_extensions/src_py3/test_typing_extensions.py

@@ -1448,6 +1448,15 @@ def close(self):
             self.assertIsSubclass(B, Custom)
             self.assertNotIsSubclass(A, Custom)
 
+        def test_no_init_same_for_different_protocol_implementations(self):
+            class CustomProtocolWithoutInitA(Protocol):
+                pass
+
+            class CustomProtocolWithoutInitB(Protocol):
+                pass
+
+            self.assertEqual(CustomProtocolWithoutInitA.__init__, CustomProtocolWithoutInitB.__init__)
+
 
 class TypedDictTests(BaseTestCase):
 

typing_extensions/src_py3/typing_extensions.py

@@ -1151,6 +1151,11 @@ def _is_callable_members_only(cls):
 if hasattr(typing, 'Protocol'):
     Protocol = typing.Protocol
 elif HAVE_PROTOCOLS and not PEP_560:
+
+    def _no_init(self, *args, **kwargs):
+        if type(self)._is_protocol:
+            raise TypeError('Protocols cannot be instantiated')
+
     class _ProtocolMeta(GenericMeta):
         """Internal metaclass for Protocol.
 
@@ -1241,9 +1246,6 @@ def __init__(cls, *args, **kwargs):
                         raise TypeError('Protocols can only inherit from other'
                                         ' protocols, got %r' % base)
 
-                def _no_init(self, *args, **kwargs):
-                    if type(self)._is_protocol:
-                        raise TypeError('Protocols cannot be instantiated')
                 cls.__init__ = _no_init
 
             def _proto_hook(other):
@@ -1398,6 +1400,10 @@ def __new__(cls, *args, **kwds):
 elif PEP_560:
     from typing import _type_check, _GenericAlias, _collect_type_vars  # noqa
 
+    def _no_init(self, *args, **kwargs):
+        if type(self)._is_protocol:
+            raise TypeError('Protocols cannot be instantiated')
+
     class _ProtocolMeta(abc.ABCMeta):
         # This metaclass is a bit unfortunate and exists only because of the lack
         # of __instancehook__.
@@ -1574,10 +1580,6 @@ def _proto_hook(other):
                         isinstance(base, _ProtocolMeta) and base._is_protocol):
                     raise TypeError('Protocols can only inherit from other'
                                     ' protocols, got %r' % base)
-
-            def _no_init(self, *args, **kwargs):
-                if type(self)._is_protocol:
-                    raise TypeError('Protocols cannot be instantiated')
             cls.__init__ = _no_init