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bpo-44806: Fix __init__ in subclasses of protocols #27545

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Merged
merged 1 commit into from
Aug 2, 2021
Merged

bpo-44806: Fix __init__ in subclasses of protocols #27545

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36 changes: 36 additions & 0 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -881,6 +881,9 @@ 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
Expand All @@ -895,6 +898,8 @@ 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
Expand Down Expand Up @@ -1322,6 +1327,37 @@ 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')
Expand Down
12 changes: 10 additions & 2 deletions Lib/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1381,8 +1381,7 @@ 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:
Expand Down Expand Up @@ -1522,6 +1521,15 @@ 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.
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2021-08-02-14-37-32.bpo-44806.wOW_Qn.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Non-protocol subclasses of :class:`typing.Protocol` ignore now the
``__init__`` method inherited from protocol base classes.