bpo-44806: Fix __init__ in subclasses of protocols (GH-27545)
Non-protocol subclasses of protocol ignore now the __init__ method
inherited from protocol base classes.
(cherry picked from commit 043cd60abed09edddc7185bcf7d039771acc734d)
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 3d9a347..6e557c4 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -875,6 +875,9 @@ class P(Protocol): pass
class C(P): pass
self.assertIsInstance(C(), C)
+ with self.assertRaises(TypeError):
+ C(42)
+
T = TypeVar('T')
class PG(Protocol[T]): pass
@@ -889,6 +892,8 @@ class PG(Protocol[T]): pass
class CG(PG[T]): pass
self.assertIsInstance(CG[int](), CG)
+ with self.assertRaises(TypeError):
+ CG[int](42)
def test_cannot_instantiate_abstract(self):
@runtime_checkable
@@ -1316,6 +1321,37 @@ def __init__(self):
self.assertEqual(C[int]().test, 'OK')
+ class B:
+ def __init__(self):
+ self.test = 'OK'
+
+ class D1(B, P[T]):
+ pass
+
+ self.assertEqual(D1[int]().test, 'OK')
+
+ class D2(P[T], B):
+ pass
+
+ self.assertEqual(D2[int]().test, 'OK')
+
+ def test_new_called(self):
+ T = TypeVar('T')
+
+ class P(Protocol[T]): pass
+
+ class C(P[T]):
+ def __new__(cls, *args):
+ self = super().__new__(cls, *args)
+ self.test = 'OK'
+ return self
+
+ self.assertEqual(C[int]().test, 'OK')
+ with self.assertRaises(TypeError):
+ C[int](42)
+ with self.assertRaises(TypeError):
+ C[int](a=42)
+
def test_protocols_bad_subscripts(self):
T = TypeVar('T')
S = TypeVar('S')
diff --git a/Lib/typing.py b/Lib/typing.py
index e492bd2..6f884e1 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1379,8 +1379,7 @@ def _is_callable_members_only(cls):
def _no_init(self, *args, **kwargs):
- if type(self)._is_protocol:
- raise TypeError('Protocols cannot be instantiated')
+ raise TypeError('Protocols cannot be instantiated')
def _caller(depth=1, default='__main__'):
try:
@@ -1523,6 +1522,15 @@ def _proto_hook(other):
# We have nothing more to do for non-protocols...
if not cls._is_protocol:
+ if cls.__init__ == _no_init:
+ for base in cls.__mro__:
+ init = base.__dict__.get('__init__', _no_init)
+ if init != _no_init:
+ cls.__init__ = init
+ break
+ else:
+ # should not happen
+ cls.__init__ = object.__init__
return
# ... otherwise check consistency of bases, and prohibit instantiation.