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TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

Combative Constrictor answered on November 7, 2023 Popularity 6/10 Helpfulness 3/10

answer TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

Comment

TypeError: metaclass conflict

class M1(type): pass
class M2(type): pass

class A1(metaclass=M1): pass
class A2(metaclass=M2): pass

class B1(A1, metaclass=M2): pass  # Mypy Error: metaclass conflict
# At runtime the above definition raises an exception
# TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

class B12(A1, A2): pass  # Mypy Error: metaclass conflict

# This can be solved via a common metaclass subtype:
class CorrectMeta(M1, M2): pass
class B2(A1, A2, metaclass=CorrectMeta): pass  # OK, runtime is also OK

Popularity 6/10 Helpfulness 3/10 Language typescript

Source: mypy.readthedocs.io

Tags: derived-class metaclass subclass typescript

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