itertools模块在python中处理可迭代的对象很方便。
itertools模块方法
itertools.dropwhile
参数 predicate, iterable
创建一个迭代器，只要函数predicate(item)为True，就丢弃iterable中的项，如果predicate返回False，就会生成iterable中的项和所有后续项。
等价实现:
def dropwhile(predicate, iterable):
iterable = iter(iterable)
for x in iterable:
if not predicate(x):
yield x
break
for x in iterable:
yield x使用示例
from itertools import dropwhile
def should_drop(x):
print 'test:', x
return (x < 1)
for i in dropwhile(should_drop, [-1, 0, 1, 2, 3, 4, 1, -2]):
print 'yield', i
Test: -1
Test: 0
Test: 1
Yield: 1
Yield: 2
Yield: 3
yield: 4
yield: 1
yield: -2 takewhile
创建一个迭代器，生成iterable中predicate(item)为True的项，只要predicate计算为False，迭代就会立即停止。 即：从序列的头开始，直到执行函数func失败。
def takewhile(predicate, iterable):
for x in iterable:
if predicate(x):
yield x
else:
break使用
from itertools import *
def should_take(x):
print 'Testing:', x
return (x < 2)
for i in takewhile(should_take, [-1, 0, 1, 2, 3, 4, 1, -2]):
print 'Yielding:', i
Testing: -1
Yielding: -1
Testing: 0
Yielding: 0
Testing: 1
Yielding: 1
Testing: 2