bpo-45121: Fix RecursionError when calling Protocol.__init__ from a subclass' __init__ (GH-28206) (GH-28232)
(cherry picked from commit c11956a8bddd75f02ccc7b4da7e4d8123e1f3c5f)
Co-authored-by: Yurii Karabas <1998uriyyo@gmail.com>
diff --git a/Lib/typing.py b/Lib/typing.py
index 24f834e..5873d53 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1404,6 +1404,11 @@ def _no_init_or_replace_init(self, *args, **kwargs):
if cls._is_protocol:
raise TypeError('Protocols cannot be instantiated')
+ # Already using a custom `__init__`. No need to calculate correct
+ # `__init__` to call. This can lead to RecursionError. See bpo-45121.
+ if cls.__init__ is not _no_init_or_replace_init:
+ return
+
# 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__`