Can I avoid the ```metaclass=``` when I define an inherited class?

Question

I would like to have a custom metaclass that looks like the definition of a TypedDict.

When one declares a new TypedDict we write something like this:

from typing import TypedDict

class MyClass(TypedDict, total=False):
  pass

However, when I declare a metaclass, it looks like this:

class MetaSerial(type):
  def __new__(pls, name, bases, act, exclude: list[str] = [], custom: list[str] = []):
    dct["_exclude"] = exclude
    dct["_custom"] = custom
    return super().__new__(cls, name, bases, dct)

class Serial(metaclass=MetaSerial, exclude=["value"], custom=["terminals"]):
  pass

So, the million dollar question is: is there a way for me to get rid of the annoying metaclass= and use something like:

class Serial(MetaSerial, exclude=["value"], custom=["terminals"]):
  pass

Answer 1

Avoid metaclasses where possible (every metaclass you define is a potential conflict with another metaclass). All you need here is a base class with an appropriate __init_subclass__ method.

class SerialBase:
    def __init_subclass__(cls, exclude: list[str] = None, custom: list[str] = None, **kwargs):
        super().__init_subclass__(**kwargs)
        if exclude is None:
            exclude = []

        if custom is None:
            custom = []

        cls._exclude = exclude
        cls._custom = custom

class Serial(SerialBase, exclude=["value"], custom=["terminals"]):
    pass