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缘由：

同事需要实现一个功能：从指定IP段中排除某些IP或IP段，最后得到一个类似于IP区间的结果格式。比如：

$ python py_exclude_ip_cidr.py 10.32.0.0/16 10.32.0.0/24 10.32.26.254 10.32.104.199
10.32.1.0-10.32.26.253
10.32.26.255-10.32.104.198
10.32.104.200-10.32.255.255

正文：

理清思路：

将CIDR格式的IP段转换成大整数区间的格式，然后再从这个大区间中剔除「要排除的小区间」，然后将区间的首尾整数转换成IP地址的格式。

提取出的问题：

其中碰到的一个问题就是，将一个「不一定连续」的有序列表转换成「一个或多个」连续有序列表。

参考解答：

实现一个函数myfunc，传入不一定连续的列表，返回一个包含多个区间的列表，比如：

myfunc([2, 3, 4, 5, 12, 13, 14, 15, 16, 17, 20])

返回：

[(2,5), (12,17), 20]

==

from operator import itemgetter
from itertools import groupby

ranges = []
data = [2, 3, 4, 5, 12, 13, 14, 15, 16, 17]
for k, g in groupby(enumerate(data), lambda (i,x):i-x):
    group = map(itemgetter(1), g)
    ranges.append((group[0], group[-1]))
    print group
print ranges

>>> # Show a dictionary sorted and grouped by value（Python中根据dict中元素出现的次数进行分组）
>>> from operator import itemgetter
>>> d = dict(a=1, b=2, c=1, d=2, e=1, f=2, g=3)
>>> di = sorted(d.iteritems(), key=itemgetter(1))
>>> for k, g in groupby(di, key=itemgetter(1)):
...     print k, map(itemgetter(0), g)
...
1 ['a', 'c', 'e']
2 ['b', 'd', 'f']
3 ['g']

>>> # Find runs of consecutive numbers using groupby.  The key to the solution
>>> # is differencing with a range so that consecutive numbers all appear in
>>> # same group.（将list中连续的串进行分组）
>>> data = [ 1,  4,5,6, 10, 15,16,17,18, 22, 25,26,27,28]
>>> for k, g in groupby(enumerate(data), lambda (i,x):i-x):
...     print map(itemgetter(1), g)
...
[1]
[4, 5, 6]
[10]
[15, 16, 17, 18]
[22]
[25, 26, 27, 28]

参考链接：

• http://stackoverflow.com/questions/2154249/identify-groups-of-continuous-numbers-in-a-list
• http://stackoverflow.com/questions/2361945/detecting-consecutive-integers-in-a-list
• http://stackoverflow.com/questions/16315189/python-find-incremental-numbered-sequences-with-a-list-comprehension
• http://stackoverflow.com/questions/3429510/pythonic-way-to-convert-a-list-of-integers-into-a-string-of-comma-separated-rang
• http://stackoverflow.com/questions/10420464/group-list-of-ints-by-continuous-sequence
• http://stackoverflow.com/questions/33402355/finding-groups-of-increasing-numbers-in-a-list
• https://docs.python.org/2.6/library/itertools.html#examples

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