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pymotw 链接
无限迭代器
itertools.count()
说明
生成一个无限迭代的数字队列, 只有进行
参数
其实数字以及步幅
start, [step]
返回值
start, start+step, start+2*step, ...
示例
count(10) --> 10 11 12 13 14 ...
from itertools import *
import time
c = count(10,5)
print c
for i in c:
time.sleep(0.5)
print i
"""
count(10, 5)
10
15
20
25
30
35
40
45
50
55
Process finished with exit code -1
"""
详细示例
itertools.cycle()
说明
传入一个可迭代对象然后循环遍历此对象
参数
p
返回值
p0, p1, ... plast, p0, p1, ...
示例
cycle('ABCD') --> A B C D A B C D ...
from itertools import *
import time
c = cycle([1, 2, 3])
print c
for i in c:
time.sleep(0.5)
print i
"""
<itertools.cycle object at 0x0000000002A42088>
1
2
3
1
2
3
1
2
Process finished with exit code -1
"""
详细示例
itertools.repeat()
说明
传入一个对象, 以及数字, 遍历此对象指定数字次数
参数
elem [,n]
返回值
elem, elem, elem, ... endlessly or up to n times
示例
repeat(10, 3) --> 10 10 10
from itertools import *
import time
c = repeat(3, 5)
print c
for i in c:
time.sleep(0.5)
print i
"""
repeat(3, 5)
3
3
3
3
3
Process finished with exit code 0
"""
详细示例
处理输入序列迭代器
itertools.chain()
说明
传入多个序列, 遍历时将多个序列串联一起进行
参数
p, q, ...
返回值
p0, p1, ... plast, q0, q1, ...
示例
chain('ABC', 'DEF') --> A B C D E F
from itertools import *
c = chain(range(5), range(3))
print c
for i in c:
print i
"""
<itertools.chain object at 0x0000000002A77FD0>
0
1
2
3
4
0
1
2
Process finished with exit code 0r
"""
详细示例
itertools.compress()
说明
参数传入一个序列以及一个选择列表，对数据序列基于选择列表进行筛选
参数
data, selectors
返回值
(d[0] if s[0]), (d[1] if s[1]), ...
示例
compress('ABCDEF', [1,0,1,0,1,1]) --> A C E F
from itertools import *
c = compress("hahahahahaha", [1, 0, 1, 0, 1, 0, 1, 0])
print c
for i in c:
print i
"""
<itertools.compress object at 0x0000000002B01048>
h
h
h
h
Process finished with exit code 0
"""
详细示例
itertools.dropwhile()
说明
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。
即：在条件为false之后的第一次, 返回迭代器中剩下来的项.
参数
pred, seq
返回值
seq[n], seq[n+1], starting when pred fails
示例
dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1
def dropwhile(predicate, iterable):
# dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1
iterable = iter(iterable)
for x in iterable:
if not predicate(x):
yield x
break
for x in iterable:
yield x
from itertools import *
def should_drop(x):
print 'Testing:', x
return (x<1)
for i in dropwhile(should_drop, [ -1, 0, 1, 2, 3, 4, 1, -2 ]):
print 'Yielding:', i
Testing: -1
Testing: 0
Testing: 1
Yielding: 1
Yielding: 2
Yielding: 3
Yielding: 4
Yielding: 1
Yielding: -2
详细示例
itertools.groupby()
说明
按照keyfunc函数对序列每个元素执行后的结果分组(每个分组是一个迭代器), 返回这些分组的迭代器
参数
iterable[, keyfunc]
返回值
sub-iterators grouped by value of keyfunc(v)
示例
chain('ABC', 'DEF') --> A B C D E F
迭代器 参数 结果 例子
ifilter() pred, seq elements of seq where pred(elem) is True ifilter(lambda x: x%2, range(10)) --> 1 3 5 7 9
ifilterfalse() pred, seq elements of seq where pred(elem) is False ifilterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8
islice() seq, [start,] stop [, step] elements from seq[start:stop:step] islice('ABCDEFG', 2, None) --> C D E F G
imap() func, p, q, ... func(p0, q0), func(p1, q1), ... imap(pow, (2,3,10), (5,2,3)) --> 32 9 1000
starmap() func, seq func(*seq[0]), func(*seq[1]), ... starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000
tee() it, n it1, it2 , ... itn splits one iterator into n
takewhile() pred, seq seq[0], seq[1], until pred fails takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4
izip() p, q, ... (p[0], q[0]), (p[1], q[1]), ... izip('ABCD', 'xy') --> Ax By
izip_longest() p, q, ... (p[0], q[0]), (p[1], q[1]), ... izip_longest('ABCD', 'xy', fillvalue='-') --> Ax By C- D-