Python - dir(list) -- __functions__它们是什么?

Question

>>> dir(list) 
['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

需要知道它在python脚本中的使用方式吗？我们是否必须编写一个类并将它们用作方法或如何？有人可以用简单的例子来解释我吗？

Answer 1

是python的"协议"或"dunder(双下划线(方法"或"魔术方法"。用于特殊的 python 操作，例如__add__(self, other)定义调用self + other时会发生什么，__str__(self)定义调用str(self)时会发生什么。

https://rszalski.github.io/magicmethods/

https://docs.python.org/3/reference/datamodel.html#special-method-names

---

例：

In [19]: class Adder:
...:     def __init__(self, x):
...:         print('in __init__')
...:         self.x = x
...: 
...:     def __add__(self, other):
...:         print('in __add__')
...:         return self.x + other
...: 
...:     def __str__(self):
...:         print('in __str__')
...:         return 'Adder({})'.format(self.x)
...: 
...:     def __call__(self, value):
...:         print('in __call__')
...:         return self + value
...:     
In [20]: a = Adder(3)
in __init__
In [21]: a.x
Out[21]: 3
In [22]: a + 12
in __add__
Out[22]: 15
In [23]: str(a)
in __str__
Out[23]: 'Adder(3)'
In [24]: a(3)
in __call__
in __add__
Out[24]: 6