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Less harsh implementation for issubclass() #15394

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5 changes: 3 additions & 2 deletions Lib/_py_abc.py
Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
from _weakrefset import WeakSet

from warnings import warn

def get_cache_token():
"""Returns the current ABC cache token.
Expand Down Expand Up @@ -108,7 +108,8 @@ def __instancecheck__(cls, instance):
def __subclasscheck__(cls, subclass):
"""Override for issubclass(subclass, cls)."""
if not isinstance(subclass, type):
raise TypeError('issubclass() arg 1 must be a class')
warn('issubclass() arg 1 is not a class. Returning False.')
return False
# Check cache
if subclass in cls._abc_cache:
return True
Expand Down