Question

Normally, a base class method in Python can be called from a derived class the same way any derived class function is called:

class Base:
    def base_method(self):
        print("Base method")

class Foo(Base):
    def __init__(self):
        pass

f = Foo()
f.base_method()

However, when I create a class dynamically using the type function, I am unable to call base class methods without passing in a self instance:

class Base:
    def base_method(self):
        print("Base method")

f = type("Foo", (Base, object), { "abc" : "def" })
f.base_method() # Fails

This raises a TypeError: TypeError: base_method() takes exactly 1 argument (0 given)

It works if I explicitly pass a self parameter:

f.base_method(f)

Why is it necessary to explicitly pass the self instance when calling a base class method?

Answer 1

Your line f = type(...) returns a class, not an instance.

If you do f().base_method(), it should work.