Python的 for 循环
for 循环与其它大多数语言一样，Python 也拥有 for 循环。你到现在还未曾看到它们的唯一原因就是，Python 在其它太多的方面表现出色，通常你不需要它们。
>>> li = ['a', 'b', 'e']
>>> for s in li:
... print s
a
b
e
>>> print "\n".join(li)
a
b
e
>>> for i in range(5):
... print i
0
1
2
3
4
>>> li = ['a', 'b', 'c', 'd', 'e']
>>> for i in range(len(li)):
... print li
a
b
c
d
e
>>> import os
>>> for k, v in os.environ.items():
... print "%s=%s" % (k, v)
USERPROFILE=C:\Documents and Settings\mpilgrim
OS=Windows_NT
COMPUTERNAME=MPILGRIM
USERNAME=mpilgrim
[...略...]
>>> print "\n".join(["%s=%s" % (k, v)
... for k, v in os.environ.items()])
USERPROFILE=C:\Documents and Settings\mpilgrim
OS=Windows_NT
COMPUTERNAME=MPILGRIM
USERNAME=mpilgrim
[...略...]
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