class needs to refer a different class

[Gribouillis]

the objective is to return an instance of file class instead of an instance of itself

I'm not sure I understand what you are trying to do but calling a class' constructor to get an object of a different type seems completely inappropriate. More specifically, __init__() methods don't even use the return statement in Python.

You could achieve the same (misleading) effect by overwriting the name of the class

class Foo:
    pass

class Bar:
    pass

_c_foo = Foo

def Foo(condition):
    if condition:
        return _c_foo()
    else:
        return Bar()

if __name__ == '__main__':
    f = Foo(0) # returns a Bar instance while pretending to create a Foo instance.