class Pizza(object): def __init__(self, size): self.size = size def get_size(self): return self.size #Pizza.get_size # <function __main__.Pizza.get_size> #Pizza.get_size() # TypeError: get_size() missing 1 required positional argument: 'self' #Pizza.get_size(Pizza(42)) # 42 Pizza(42).get_size() # 42 m = Pizza(42).get_size m.__self__ # <__main__.Pizza at 0x7f8ca4755048> m == m.__self__.get_size # True