python 黑色幽默

• 旧式类 VS 新式类

Old：

>>> class X():pass
>>> print type(X())
>>> <type 'instance'>

New：

>>> class X(object):pass
>>> print type(X())
>>> <class '__mian__.X'>

Let's go

>>> class X():pass
>>> class Y():pass
>>> print type(X()) == type(Y())
>>> True
>>> class X(object):pass
>>> class Y(object):pass
>>> print type(X()) == type(Y())
>>> False

• 内建函数

  • __missing__

  被 __getitem__ 调用.

  Let's go

        >>> class DefaultDict(dict):
        >>>   def __getitem__(self, key):
        >>>     print '__getitem__:', key
        >>>     return super(Dict , self).__getitem__(key)
        >>>   def __missing__(self, key):
        >>>     print '__missing__'
        >>> print DefaultDict()['a']
        >>> __getitem__: a
        >>> __missing__
        >>> None
        >>> dict()['a']      
        >>> KeyError: 'a'
  

### OtherWays
`dict. setdefault(key[, default])` 也可以解决
`class collections.defaultdict([default_factory[, ...]])`更好。

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To Be Continue