python - 不能继承timedelta

Question

我对 timedelta 感到恼火。没有__format__方法。所以我想继承timedelta (built-in/extension type 'datetime.timedelta' 没有猴子补丁选项)

所以我厌倦了继承(my_dict仅供引用；这个有效!)。

from datetime import timedelta

class my_dict(dict):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

class my_timedelta(timedelta):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

print(my_dict.__mro__)
# (<class '__main__.my_dict'>, <class 'dict'>, <class 'object'>)

print(my_timedelta.__mro__)
# (<class '__main__.my_timedelta'>,
#  <class 'datetime.timedelta'>, <class 'object'>)

d0 = my_dict(); d1 = my_dict(a=3)
print(d0, d1)
# -> {} {'a': 3}

# no arguments: this works!
t0 = my_timedelta()
print(t0)      # -> 0:00:00

# one argument: TypeError
# t1 = my_timedelta(5)  # -> TypeError: object.__init__() takes no parameters
# print(t1)

# a key-word argument: TypeError
# t2 = my_timedelta(seconds=5)  # -> TypeError: object.__init__() 
#                                               takes no parameters
# print(t2)

两者的方法解析顺序看起来很相似；但似乎__init__在 timedelta案例正在跳过 timedelta.__init__并将目录跳转到 object.__init__ .

我做错了什么吗？我如何继承 timedelta ？这里出了什么问题？

Answer 1

根据How to initialize an inherited object with either the 'usual' (keyword) arguments or an instance of the parent ，您必须重写 new() 方法。像这样的东西:

class my_timedelta(timedelta):
    def __new__(cls, *args, **kwargs):
        # whatever here
        return super().__new__(cls, *args, **kwargs)