Python: creating class instance without calling initializer

Question

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

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)
>>> 

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:

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())

Answer 1

Pass another argument to the constructor, like so:

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

You can then call it like this:

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

Also, I'm not sure it's allowed to name both the field and the method __simple. If only for readability, you should change that.

Answer 2

When feasible, letting __init__ get called (and make the call innocuous by suitable arguments) is preferable. However, should that require too much of a contortion, you do have an alternative, as long as you avoid the disastrous choice of using old-style classes (there is no good reason to use old-style classes in new code, and several good reasons not to)...:

   class String(object):
      ...

   bare_s = String.__new__(String)

This idiom is generally used in classmethods which are meant to work as "alternative constructors", so you'll usually see it used in ways such as...:

@classmethod 
def makeit(cls):
    self = cls.__new__(cls)
    # etc etc, then
    return self

(this way the classmethod will properly be inherited and generate subclass instances when called on a subclass rather than on the base class).