Python：创建类实例而不调用initializer [英] Python: creating class instance without calling initializer

问题描述

有没有办法避免在初始化类时调用 __ init __ ，例如从类方法调用

Is there any way to avoid calling __init__ on a class while initializing it, such as from a class method?

我试图在Python中创建一个case和标点符号不敏感的字符串类用于有效的比较目的，但是无法创建一个新的实例，而不调用 __ init __ 。

I am trying to create a case and punctuation insensitive string class in Python used for efficient comparison purposes but am having trouble creating a new instance without calling __init__.

>>> class String:

    def __init__(self, string):
        self.__string = tuple(string.split())
        self.__simple = tuple(self.__simple())

    def __simple(self):
        letter = lambda s: ''.join(filter(lambda s: 'a' <= s <= 'z', s))
        return filter(bool, map(letter, map(str.lower, self.__string)))

    def __eq__(self, other):
        assert isinstance(other, String)
        return self.__simple == other.__simple

    def __getitem__(self, key):
        assert isinstance(key, slice)
        string = String()
        string.__string = self.__string[key]
        string.__simple = self.__simple[key]
        return string

    def __iter__(self):
        return iter(self.__string)

>>> String('Hello, world!')[1:]
Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    String('Hello, world!')[1:]
  File "<pyshell#1>", line 17, in __getitem__
    string = String()
TypeError: __init__() takes exactly 2 positional arguments (1 given)
>>> 

我应该替换 string = String string .__ string = self .__ string [key]; string .__ simple = self .__ simple [key] 使用切片初始化新对象？

What should I replace string = String(); string.__string = self.__string[key]; string.__simple = self.__simple[key] with to initialize the new object with the slices?

EDIT：

由于下面的答案的启发，初始化程序已经被编辑以快速检查没有参数。

As inspired by the answer written below, the initializer has been edited to quickly check for no arguments.

def __init__(self, string=None):
    if string is None:
        self.__string = self.__simple = ()
    else:
        self.__string = tuple(string.split())
        self.__simple = tuple(self.__simple())

推荐答案

在这个例子中使用元类提供了一个很好的解决方案。元类有限的使用，但工作正常。

Using a metaclass provides a nice solution in this example. The metaclass has limited use but works fine.

>>> class MetaInit(type):

    def __call__(cls, *args, **kwargs):
        if args or kwargs:
            return super().__call__(*args, **kwargs)
        return cls.__new__(cls)

>>> class String(metaclass=MetaInit):

    def __init__(self, string):
        self.__string = tuple(string.split())
        self.__simple = tuple(self.__simple())

    def __simple(self):
        letter = lambda s: ''.join(filter(lambda s: 'a' <= s <= 'z', s))
        return filter(bool, map(letter, map(str.lower, self.__string)))

    def __eq__(self, other):
        assert isinstance(other, String)
        return self.__simple == other.__simple

    def __getitem__(self, key):
        assert isinstance(key, slice)
        string = String()
        string.__string = self.__string[key]
        string.__simple = self.__simple[key]
        return string

    def __iter__(self):
        return iter(self.__string)

>>> String('Hello, world!')[1:]
<__main__.String object at 0x02E78830>
>>> _._String__string, _._String__simple
(('world!',), ('world',))
>>> 

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