enumerate的用法

时间：2010-03-13 来源：flyaway57

  enumerate(iterable) -> iterator for index, value of iterable

  Return an enumerate object.  iterable must be an other object that supports
  iteration.  The enumerate object yields pairs containing a count (from
  zero) and a value yielded by the iterable argument.  enumerate is useful
  for obtaining an indexed list: (0, seq[0]), (1, seq[1]), (2, seq[2]), ...

返回一个enumerate类。可迭代的对象必须是其他支持迭代的类。（这句话保留）。enumerate在得到一个索引
的序列上非常有用

这个是enumerate的定义

def enumerate(collection):
        'Generates an indexed series: (0,coll[0]), (1,coll[1]) ...'
        i = 0
        it = iter(collection)
        while 1:
            yield (i, it.next())
            i += 1

以前在python中，找出一个序列的index和value，需要这样做：

for i in range(len(alist)):
print i, alist[i]

现在，只需要用一个enumerate即可：

for index, value in enumerate(alist):
print index, value

可以讲enumerate用到统计文件的行数上

>>> for count, line in enumerate(open('haha')):
... pass
...
>>> print count+1

下面还有两种办法
1

>>> count = len(open('haha').readlines())
>>> print count

>>> len(list(i for line in open('haha')))