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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