TypeError: 'int' object is not callable

What it does

Checks for arguments to metaclass= that are invalid.

Why is this bad?

Python allows arbitrary expressions to be used as the argument to metaclass=. These expressions, however, need to be callable and accept the same arguments as type.__new__.

Example

# TypeError: 'int' object is not callable
class B(metaclass=42): ...  # error

References

• Python documentation: Metaclasses