bpo-45081: Fix __init__ method generation when inheriting from Protocol (GH-28121)
Co-authored-by: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>
(cherry picked from commit 0635e201beaf52373f776ff32702795e38f43ae3)
Co-authored-by: Yurii Karabas <1998uriyyo@gmail.com>
diff --git a/Lib/typing.py b/Lib/typing.py
index 4c2d9fc..24f834e 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1398,8 +1398,29 @@ def _is_callable_members_only(cls):
return all(callable(getattr(cls, attr, None)) for attr in _get_protocol_attrs(cls))
-def _no_init(self, *args, **kwargs):
- raise TypeError('Protocols cannot be instantiated')
+def _no_init_or_replace_init(self, *args, **kwargs):
+ cls = type(self)
+
+ if cls._is_protocol:
+ raise TypeError('Protocols cannot be instantiated')
+
+ # Initially, `__init__` of a protocol subclass is set to `_no_init_or_replace_init`.
+ # The first instantiation of the subclass will call `_no_init_or_replace_init` which
+ # searches for a proper new `__init__` in the MRO. The new `__init__`
+ # replaces the subclass' old `__init__` (ie `_no_init_or_replace_init`). Subsequent
+ # instantiation of the protocol subclass will thus use the new
+ # `__init__` and no longer call `_no_init_or_replace_init`.
+ for base in cls.__mro__:
+ init = base.__dict__.get('__init__', _no_init_or_replace_init)
+ if init is not _no_init_or_replace_init:
+ cls.__init__ = init
+ break
+ else:
+ # should not happen
+ cls.__init__ = object.__init__
+
+ cls.__init__(self, *args, **kwargs)
+
def _caller(depth=1, default='__main__'):
try:
@@ -1542,15 +1563,6 @@ 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.
@@ -1561,7 +1573,7 @@ def _proto_hook(other):
issubclass(base, Generic) and base._is_protocol):
raise TypeError('Protocols can only inherit from other'
' protocols, got %r' % base)
- cls.__init__ = _no_init
+ cls.__init__ = _no_init_or_replace_init
class _AnnotatedAlias(_GenericAlias, _root=True):