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def NamedTuple(s):
    """Returns a new subclass of tuple with named fields.

    >>> Point = NamedTuple('Point x y')
    >>> Point.__doc__           # docstring for the new class
    'Point(x, y)'
    >>> p = Point(11, y=22)     # instantiate with positional args or keywords
    >>> p[0] + p[1]             # works just like the tuple (11, 22)
    33
    >>> p.x + p.y               # fields also accessable by name
    33
    >>> p                       # readable __repr__ with name=value style
    Point(x=11, y=22)

    """

f = s.split()
typename, field_names = f[0], f[1:]
nargs = len(field_names)


def __new__(cls, *args, **kwds):
if kwds:
try:
args += tuple(kwds[name] for name in field_names[len(args):])
except KeyError, name:
raise TypeError('%s missing required argument: %s' % (typename, name))
if len(args) != nargs:
raise TypeError('%s takes exactly %d arguments (%d given)' % (typename,
nargs, len(args)))
return tuple.__new__(cls, args)


template = '%s(%s)' % (typename, ', '.join('%s=%%r' % name for name
infield_names))


def __repr__(self, show=template.__mod__):
return show(self)


m = dict(vars(tuple)) # pre-lookup superclass methods (for faster lookup)
m.update(__doc__= '%s(%s)' % (typename, ', '.join(field_names)),
__slots__ = (), # no per-instance dict (so instances are same size as
tuples)
__new__ = __new__,
__repr__ = __repr__,
)
m.update((name, property(itemgetter(index))) for index, name
inenumerate(field_names))


return type(typename, (tuple,), m)

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On 1/31/07, 俊杰蔡 <yzcaijunjie at gmail.com> wrote:
>
> 以下是我从例程中摘录的一个方法：
>
> def NamedTuple(s):
>     """Returns a new subclass of tuple with named fields.
>
>     >>> Point = NamedTuple('Point x y')
>     >>> Point.__doc__           # docstring for the new class
>     'Point(x, y)'
>     >>> p = Point(11, y=22)     # instantiate with positional args or keywords
>     >>> p[0] + p[1]             # works just like the tuple (11, 22)
>     33
>     >>> p.x + p.y               # fields also accessable by name
>     33
>     >>> p                       # readable __repr__ with name=value style
>     Point(x=11, y=22)
>
>     """
>
> f = s.split()
>
> typename, field_names = f[0], f[1:]
>
> nargs = len(field_names)
>
>
>
> def __new__(cls, *args, **kwds):
>
> if kwds:
>
> try:
>
> args += tuple(kwds[name] for name in field_names[len(args):])
>
> except KeyError, name:
>
> raise TypeError('%s missing required argument: %s' % (typename, name))
>
> if len(args) != nargs:
>
> raise TypeError('%s takes exactly %d arguments (%d given)' % (typename,
> nargs, len(args)))
>
> return tuple.__new__(cls, args)
>
>
>
> template = '%s(%s)' % (typename, ', '.join('%s=%%r' % name for name in
> field_names))
>
>
>
> def __repr__(self, show=template.__mod__):
>
> return show(self)
>
>
>
>
> m = dict(vars(tuple)) # pre-lookup superclass methods (for faster lookup)
>
> m.update(__doc__= '%s(%s)' % (typename, ', '.join(field_names)),
>
> __slots__ = (), # no per-instance dict (so instances are same size as
> tuples)
>
> __new__ = __new__,
>
> __repr__ = __repr__,
>
> )
>
> m.update((name, property(itemgetter(index))) for index, name inenumerate(field_names))
>
>
>
> return type(typename, (tuple,), m)
>
>
> 我对其中几个部分不懂：
>
> 1  在方法NamedTuple(s)中定义__new__()和__repar__()是重载么？如果是，重载不需要在类中进行么？
> 2  __new__()和__repar__()各自在什么时候被调用？
> 3 有很多的__slots__ ，__new__， __repr__系统变量，这些变量改怎么来了解他们的用途么？
>
>
> 学习ing
>
> _______________________________________________
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注意最后一句：
type(typename, (tuple,), m)

这是 metaclass 的范畴了，实际上：
class Temp(tuple):
    a = 1
    def test(self):pass

等价于：
def test(self):pass
Temp = type('Temp', (tuple,), {'a':1, 'test':test})

详情请看：
http://wiki.woodpecker.org.cn/moin/PythonLanguage#head-7e27906420561936f1803cf138e8504f6aa484f4


-- 
http://codeplayer.blogspot.com/
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