python itertool.groupby使用误点！

使用误点一：

误以为 groupby是按照key进行分组的：

例子

from random import choice
lst = [ Student(choice(['M','F']),choice(range(10,100))) for i in range(20)]
for k,items in itertools.groupby(lst,lambda x:x.sex):
    print k
    for x in items:
        print x
    print "-" * 20

输出结果：

FF:27F:44F:52--------------------MM:65--------------------FF:99--------------------MM:29--------------------FF:90F:20--------------------MM:63--------------------FF:93--------------------MM:53M:62M:74--------------------FF:59--------------------MM:50--------------------FF:42--------------------MM:82M:72--------------------FF:61F:86--------------------

从这里可以看出， groupby 的行为表现像uniq一样根据连续值来分组的，因此对想按照分组的key进行排序就可以达到原先的效果了

lst = sorted(lst,key=lambda x:x.sex)
for k,items in itertools.groupby(lst,lambda x:x.sex):
    print k
    for x in items:
        print x
    print "-" * 20

结果

F
F:27
F:44
F:52
F:99
F:90
F:20
F:93
F:59
F:42
F:61
F:86
--------------------
M
M:65
M:29
M:63
M:53
M:62
M:74
M:50
M:82
M:72
--------------------

参考：

https://docs.python.org/2/library/itertools.html?highlight=itertools#module-itertools