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python is obvious !

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初识 python 的时候常常会被一些陌生的概念绊倒,而当熟悉了这些概念之后你会发现它们原来是如此的简单明了!由于它们是如此的简单,所以我试图在*一*篇文章中就想把它们全部都介绍一遍。
  1. 万物皆对象,甚至一个小小的整数也不例外;而变量只是一个名字,它可以绑定到任何一个对象;使用内置函数 id 可以查看绑定的对象的 id ,语言的实现会保证两个不同对象的 id 是绝对不一样的。
    >>> a = 1
    >>> id(a)
    11541872
    >>> a = 2
    >>> id(a)
    11541860
    >>> b=1
    >>> id(b)
    11541872
  2. callable 对象
    函数、方法、类、实现了 __call__ 方法的实例对象 都是 callable 对象。callable 的意思就是在后面写个括号直接就可以进行调用了。调用内置函数 callable 可以检验一个对象是否 callable 对象。
    >>> def check(obj):
    ... if callable(obj):
    ... obj(1,2)
    ... else:
    ... print 'not a callable'
    ...
    >>> def func(a,b):print a,b
    ...
    >>> class Temp(object):
    ... def __init__(self,a,b):print a,b
    ... def __call__(self,a,b):print a,b
    ... def method(self,a,b):print a,b
    ...
    >>> check(func)
    1 2
    >>> check(Temp)
    1 2
    >>> t = Temp(1,2)
    1 2
    >>> check(t)
    1 2
    >>> check(t.method)
    1 2
    >>>
  3. 参数传递机制
    >>> def a_func(a,b,c=1,d=2):print a,b,c,d
    ...
    >>> a_func(1,2,d=4,c=3)
    1 2 3 4
    >>> a_func(1,2,3,d=4)
    1 2 3 4
    >>> a_func(1,2)
    1 2 1 2
    >>> args = (1,2)
    >>> kw = dict(c=3,d=4)
    >>> a_func(*args, **kw)
    1 2 3 4
    >>> def a_func(*args, **kw):
    ... print args
    ... print kw
    ...
    >>> a_func(1,2,d=4,c=3)
    (1, 2)
    {'c': 3, 'd': 4}
  4. docorate
    一个装饰就是一个接受一个函数作为参数的函数,它返回的还是一个函数。
    好像有点绕口,还是让代码说话吧:
    >>> def simple_log(func):
    ... def new_func(*arg, **kw):
    ... print 'enter',func.func_name
    ... func(*arg, **kw)
    ... print 'exit',func.func_name
    ... return new_func
    ...
    >>> def log(some_args):
    ... def simple_log(func):
    ... def new_func(*arg, **kw):
    ... print some_args,'enter',func.func_name
    ... func(*arg, **kw)
    ... print some_args,'exit',func.func_name
    ... return new_func
    ... return simple_log
    ...
    >>> def a_func(a,b):print a,b
    ...
    >>> simple_log(a_func)(1,2)
    enter a_func
    1 2
    exit a_func
    >>> @simple_log
    ... def a_func(a,b):print a,b
    ...
    >>> a_func(1,2)
    enter a_func
    1 2
    exit a_func
    >>> log('haha')(a_func)(1,2)
    haha enter a_func
    1 2
    haha exit a_func
    >>> @log('haha')
    ... def a_func(a,b):print a,b
    ...
    >>> a_func(1,2)
    haha enter a_func
    1 2
    haha exit a_func
  5. new style class
    继承自 object 的都是 new style class,详细内容参考这里
  6. __new__
    参考
  7. staticmethod, classmethod
    参考
  8. metaclass
    参考
    实例对象由 class 构造而成,而 class 便是由 metaclass 构造而成。
    简单地说一个 metaclass 就是一个接受三个参数(class的名字,基类tuple,class 的属性字典)的 callable 对象,它返回一个 class 。在构建 class 的时候便会调用这个 callable 对象,并使用它返回的 class 。
    所有内建类型的 metaclass 和 new style class 默认的 metaclass 都是 type
    >>> def meta(name, bases, classdict):
    ... print name
    ... print bases
    ... print classdict
    ... return type(name, bases, classdict)
    ...
    >>> class Temp(object):
    ... __metaclass__ = meta
    ... a = 1
    ... def b():pass
    ...
    Temp
    (<type object="">,)
    {'a': 1, '__module__': '__main__', 'b': <function at="" b="">, '__metaclass
    __': <function at="" meta="">}
    >>> class ATemp(Temp):
    ... __metaclass__ = meta
    ...
    ATemp
    (<class __main__.temp="">,)
    {'__module__': '__main__', '__metaclass__': <function at="" meta="">}</function></class></function></function></type>

暂时只想到这些,当然遗漏在所难免了,如有任何意见,欢迎评论 :)

update [2006-9-21]:
结合 callable 和 docorate ,其实 docorate 那个 log 的例子还可以这么写,似乎更好读一些:
>>> class log(object):
... def __init__(self, someargs):
... self.args = someargs
... def __call__(self,func):
... def new_func(*args,**kw):
... print self.args,'enter',func.func_name
... func(*args,**kw)
... print self.args,'exit',func.func_name
... return new_func
...
>>> @log('haha')
... def a_func(a,b):print a,b
...
>>> a_func(1,2)
haha enter a_func
1 2
haha exit a_func
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