In Python, how can I prohibit class inheritance? [duplicate]

Answer 1

In my opinion, classes should generally not have any subclassing restrictions at all. I would like to suggest the third option: Add a comment in your class' documentation that states that the class is not meant to be subclassed.

Answer 2

There is no Python keyword for this - it is not Pythonic.

Whether a class can be subclassed is determined by a flag called Py_TPFLAGS_BASETYPE which can be set via the C API.

This bit is set when the type can be used as the base type of another type. If this bit is clear, the type cannot be subtyped (similar to a “final” class in Java).

You can however emulate the behaviour using only Python code if you wish:

class Final(type):
    def __new__(cls, name, bases, classdict):
        for b in bases:
            if isinstance(b, Final):
                raise TypeError("type '{0}' is not an acceptable base type".format(b.__name__))
        return type.__new__(cls, name, bases, dict(classdict))

class C(metaclass=Final): pass

class D(C): pass

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