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= 带次数循环 =


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{{{David.D <dengyuanzhong@gmail.com>
reply-to	python-cn@googlegroups.com,
to	python-cn`CPyUG`华蟒用户组 <python-cn@googlegroups.com>,
date	Sat, Apr 5, 2008 at 11:55 AM
}}}subject	[CPyUG:45975] [http://groups.google.com/group/python-cn/t/8c9cada1f436b9df python的for如何获得当前循环次数？]

== 问题 ==
初学者问题：python的for如何获得当前循环次数？
我现在是这样做的：
{{{
i = 0
for item in data:
   ...
   i +=1
}}}
有更好的方法吗？

== 解答 ==
{{{
for i in range(len(data)):
  data[i]=xxx
}}}

== 深答 ==
{{{
>>> for i,v in enumerate(['a','b']):
...     print i,v
...
0 a
1 b
}}}

=== enumerate ===
 enumerate::
  * [[http://docs.python.org/lib/built-in-funcs.html|内建函式]]!
  * e.g{{{
>>> v_list_ascii=map(lambda x:chr(x),range(ord('a'),ord('z')))
>>> v_list_ascii
['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y']
>>> v_enum=enumerate(v_list_ascii)
>>> while True:
	try:
		print v_enum.next()
	except StopIteration:
		break

	
(0, 'a')
(1, 'b')
(2, 'c')
......
(23, 'x')
(24, 'y')

>>> v_enum=enumerate(v_list_ascii)
>>> for v_id,v_val in v_enum:
	print v_id,v_val

	
0 a
1 b
2 c
......
23 x
24 y
}}} example from[http://tinyurl.com/6rv22s a gift from the gods.]

##endInc

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创建 by -- ZoomQuiet [<<DateTime(2008-04-05T04:31:19Z)>>]