Python 方法

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