Question

Let’s say I have a base class defined as follows:

class Form(object):
    class Meta:
        model = None
        method = 'POST'

Now a developer comes a long and defines his subclass like:

class SubForm(Form):
    class Meta:
        model = 'User'

Now suddenly the method attribute is lost. How can I “get it back” without forcing the user to inherit his meta class from mine? Can I dynamically add a base class to Form.Meta in the initializer, or in a metaclass’s __new__ func?

Answer 1

As long as they won’t override your __init__, or it will be called (ie by super), you can monkey-patch the Meta inner class:

class Form(object):
    class Meta:
        model = None
        method = "POST"

    def __init__(self, *args, **kwargs):
        if self.__class__ != Form:
            self.Meta.__bases__ += (Form.Meta,)
        # other __init__ code here.

class SubForm(Form):
    class Meta:
        model = 'User'