042魔法方法：算术运算

人若有情死得早

1.工厂函数

>>> type(len)
<class 'builtin_function_or_method'>
>>> type(dir)
<class 'builtin_function_or_method'>
>>> type(int)
<class 'type'>
>>> type(list)
<class 'type'>
>>> class C:
        pass

>>> type(C)
<class 'type'>
>>> a = int('123')
>>> a
123
>>> b = int('456')
>>> a + b
579
>>> class New_int(int):
        def __add__(self, other):
                return int.__sub__(self, other)
        def __sub__(self, other):
                return int.__add__(self, other)

        
>>> a = New_int(3)
>>> b = New_int(5)
>>> a + b
-2
>>> a - b
8
>>> class Try_int(int):
        def __add__(self, other):
                return self + other
        def __sub__(self, other):
                return self - other

        
>>> a = Try_int(3)
>>> b = Try_int(5)
>>> a + b
Traceback (most recent call last):
  File "<pyshell#26>", line 1, in <module>
    a + b
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
  File "<pyshell#23>", line 3, in __add__
    return self + other
RuntimeError: maximum recursion depth exceeded
>>> class Try_int(int):
        def __add__(self, other):
                return int(self) + int(other)
        def __sub__(self, other):
                return int(self) - int(other)

        
>>> a = Try_int(3)
>>> b = Try_int(5)
>>> a + b
8

2.算术运算符
__add__(self, other)                  定义加法的行为：+
__sub__(self, other)                  定义减法的行为：-
__mul__(self, other)                  定义加法的行为：*
__truediv__(self, other)             定义加法的行为：/
__floordiv__(self, other)            定义加法的行为：//
__mod__(self, other)                 定义取模算法的行为：%
__divmod__(self, other)            定义当被divmod()调用时的行为
__pow__(self, other[,modulo])  定义当被power()调用或**运算时的行为
__lshift__(self, other)                 定义按位左移位的行为：<<
__rshift__(self, other)                 定义按位右移位的行为：>>
__and__(self, other)                   定义按位与操作的行为: &
__xor__(self, other)                    定义按位异或操作的行为: ^
__or__(self, other)                      定义按位或操作的行为: |