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

</pre><p></p><p>输出结果：</p>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--------------------<p>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</p><p></p><pre name="code" class="html">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