Pass class name as a variable in Python [closed]

Question

I have the below sample code:

def sample(cls):
    class a():
        def __init__(self):
            self.value='a'
    class b():
        def __init__(self):
            self.value='b'
    def __init__(self):
       self.cls=cls()
    return self.value

sample(b)

I have defined 2 classes in the sample code. I want to be able to define the class name in a function. So the above code will return 'b'. Is there a way to do it? The above code will give me the error:

'str' object is not callable