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is_init_subclass_available = hasattr(object, "__init_subclass__")
if not is_init_subclass_available:
class InitSubclassMeta(type):
"""Metaclass that implements PEP 487 protocol"""
def __new__(cls, name, bases, ns, **kwargs):
__init_subclass__ = ns.pop("__init_subclass__", None)
if __init_subclass__:
__init_subclass__ = classmethod(__init_subclass__)
ns["__init_subclass__"] = __init_subclass__
return super(InitSubclassMeta, cls).__new__(cls, name, bases, ns, **kwargs)
def __init__(cls, name, bases, ns, **kwargs):
super(InitSubclassMeta, cls).__init__(name, bases, ns)
super_class = super(cls, cls)
if hasattr(super_class, "__init_subclass__"):
super_class.__init_subclass__.__func__(cls, **kwargs)
else:
InitSubclassMeta = type # type: ignore
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