``````1、count()
>>> import itertools
>>> x = itertools.count(3)
>>> x
count(3)
>>> for i in range(10):
print(next(x), end=',')
3,4,5,6,7,8,9,10,11,12,
>>> x = itertools.count(3,5)
>>> x
count(3, 5)
>>> for i in range(10):
print(next(x), end=',')
3,8,13,18,23,28,33,38,43,48,
>>> for i in range(20):
print(next(x), end=',')
53,58,63,68,73,78,83,88,93,98,103,108,113,118,123,128,133,138,143,148,
2、cycle()
>>> x = 'abcdefg'
>>> y = itertools.cycle(x)
>>> y
<itertools.cycle object at 0x00000000031F5888>
>>> for i in range(20):
print(next(y),end=',')
a,b,c,d,e,f,g,a,b,c,d,e,f,g,a,b,c,d,e,f,
>>> for i in range(10):
print(next(y),end=',')
g,a,b,c,d,e,f,g,a,b,
>>> import itertools
>>> x = 'abcdefg'
>>> y = itertools.cycle(x)
>>> i = 0
>>> for item in y:
print(item, end=',')
i = i+1
if i>25:
break
a,b,c,d,e,f,g,a,b,c,d,e,f,g,a,b,c,d,e,f,g,a,b,c,d,e,
>>> next(y)
'f'
>>> next(y)
'g'
3、repeat()
>>> x = itertools.repeat(3)
>>> for i in range(10):
print(next(x), end=',')
3,3,3,3,3,3,3,3,3,3,
>>> for i in range(20):
print(next(x), end=',')
3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
>>> x = itertools.repeat(3,5)
>>> list(x)
[3, 3, 3, 3, 3]
4、chain()

>>> x
[0, 1, 2, 3, 4]
>>> y = range(5,10)
>>> itertools.chain(x, y)
<itertools.chain object at 0x00000000031E9BA8>
>>> list(_)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> z = ('a', 'b', 'c')
>>> list(itertools.chain(x, y, z))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 'a', 'b', 'c']
5、compress()

>>> x
range(1, 20)
>>> list(x)
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
>>> y = (1,0)*9+(1,)
>>> y
(1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1)
>>> list(itertools.compress(x, y))
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
6、groupby()

if v>10:
return 'greater than 10'
elif v<5:
return 'less than 5'
else:
return 'between 5 and 10'
>>> x = range(20)
>>> x
range(0, 20)
>>> list(x)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
>>> y = itertools.groupby(x, group)
>>> for k, v in y:
print(k, ':', list(v))
less than 5 : [0, 1, 2, 3, 4]
between 5 and 10 : [5, 6, 7, 8, 9, 10]
greater than 10 : [11, 12, 13, 14, 15, 16, 17, 18, 19]
7、zip_longest()
>>> x = range(5)
>>> y = range(8)
>>> list(zip(x, y))
[(0, 0), (1, 1), (2, 2), (3, 3), (4, 4)]
>>> list(itertools.zip_longest(x, y, fillvalue='*'))
[(0, 0), (1, 1), (2, 2), (3, 3), (4, 4), ('*', 5), ('*', 6), ('*', 7)]
>>> list(itertools.zip_longest(x, y, fillvalue='-'))
[(0, 0), (1, 1), (2, 2), (3, 3), (4, 4), ('-', 5), ('-', 6), ('-', 7)]
>>> list(itertools.zip_longest(x, y, fillvalue=9))
[(0, 0), (1, 1), (2, 2), (3, 3), (4, 4), (9, 5), (9, 6), (9, 7)]
8、product()

<itertools.product object at 0x00000000031FA870>
>>> list(_)
[(1, 4), (1, 5), (1, 6), (2, 4), (2, 5), (2, 6), (3, 4), (3, 5), (3, 6)]
>>> list(itertools.product([1,2,3],[4,5],[6,7]))
[(1, 4, 6), (1, 4, 7), (1, 5, 6), (1, 5, 7), (2, 4, 6), (2, 4, 7), (2, 5, 6), (2, 5, 7), (3, 4, 6), (3, 4, 7), (3, 5, 6), (3, 5, 7)]
>>> list(itertools.product([1,2],[4,5], repeat=3))
[(1, 4, 1, 4, 1, 4), (1, 4, 1, 4, 1, 5), (1, 4, 1, 4, 2, 4), (1, 4, 1, 4, 2, 5), (1, 4, 1, 5, 1, 4), (1, 4, 1, 5, 1, 5), (1, 4, 1, 5, 2, 4), (1, 4, 1, 5, 2, 5), (1, 4, 2, 4, 1, 4), (1, 4, 2, 4, 1, 5), (1, 4, 2, 4, 2, 4), (1, 4, 2, 4, 2, 5), (1, 4, 2, 5, 1, 4), (1, 4, 2, 5, 1, 5), (1, 4, 2, 5, 2, 4), (1, 4, 2, 5, 2, 5), (1, 5, 1, 4, 1, 4), (1, 5, 1, 4, 1, 5), (1, 5, 1, 4, 2, 4), (1, 5, 1, 4, 2, 5), (1, 5, 1, 5, 1, 4), (1, 5, 1, 5, 1, 5), (1, 5, 1, 5, 2, 4), (1, 5, 1, 5, 2, 5), (1, 5, 2, 4, 1, 4), (1, 5, 2, 4, 1, 5), (1, 5, 2, 4, 2, 4), (1, 5, 2, 4, 2, 5), (1, 5, 2, 5, 1, 4), (1, 5, 2, 5, 1, 5), (1, 5, 2, 5, 2, 4), (1, 5, 2, 5, 2, 5), (2, 4, 1, 4, 1, 4), (2, 4, 1, 4, 1, 5), (2, 4, 1, 4, 2, 4), (2, 4, 1, 4, 2, 5), (2, 4, 1, 5, 1, 4), (2, 4, 1, 5, 1, 5), (2, 4, 1, 5, 2, 4), (2, 4, 1, 5, 2, 5), (2, 4, 2, 4, 1, 4), (2, 4, 2, 4, 1, 5), (2, 4, 2, 4, 2, 4), (2, 4, 2, 4, 2, 5), (2, 4, 2, 5, 1, 4), (2, 4, 2, 5, 1, 5), (2, 4, 2, 5, 2, 4), (2, 4, 2, 5, 2, 5), (2, 5, 1, 4, 1, 4), (2, 5, 1, 4, 1, 5), (2, 5, 1, 4, 2, 4), (2, 5, 1, 4, 2, 5), (2, 5, 1, 5, 1, 4), (2, 5, 1, 5, 1, 5), (2, 5, 1, 5, 2, 4), (2, 5, 1, 5, 2, 5), (2, 5, 2, 4, 1, 4), (2, 5, 2, 4, 1, 5), (2, 5, 2, 4, 2, 4), (2, 5, 2, 4, 2, 5), (2, 5, 2, 5, 1, 4), (2, 5, 2, 5, 1, 5), (2, 5, 2, 5, 2, 4), (2, 5, 2, 5, 2, 5)]
9、permutations()、combinations()

[(1, 2, 3), (1, 2, 4), (1, 2, 5), (1, 3, 2), (1, 3, 4), (1, 3, 5), (1, 4, 2), (1, 4, 3), (1, 4, 5), (1, 5, 2), (1, 5, 3), (1, 5, 4), (2, 1, 3), (2, 1, 4), (2, 1, 5), (2, 3, 1), (2, 3, 4), (2, 3, 5), (2, 4, 1), (2, 4, 3), (2, 4, 5), (2, 5, 1), (2, 5, 3), (2, 5, 4), (3, 1, 2), (3, 1, 4), (3, 1, 5), (3, 2, 1), (3, 2, 4), (3, 2, 5), (3, 4, 1), (3, 4, 2), (3, 4, 5), (3, 5, 1), (3, 5, 2), (3, 5, 4), (4, 1, 2), (4, 1, 3), (4, 1, 5), (4, 2, 1), (4, 2, 3), (4, 2, 5), (4, 3, 1), (4, 3, 2), (4, 3, 5), (4, 5, 1), (4, 5, 2), (4, 5, 3), (5, 1, 2), (5, 1, 3), (5, 1, 4), (5, 2, 1), (5, 2, 3), (5, 2, 4), (5, 3, 1), (5, 3, 2), (5, 3, 4), (5, 4, 1), (5, 4, 2), (5, 4, 3)]
>>> list(itertools.permutations([1,2,3,4,5], 2))
[(1, 2), (1, 3), (1, 4), (1, 5), (2, 1), (2, 3), (2, 4), (2, 5), (3, 1), (3, 2), (3, 4), (3, 5), (4, 1), (4, 2), (4, 3), (4, 5), (5, 1), (5, 2), (5, 3), (5, 4)]
>>> list(itertools.permutations([1,2,3,4], 4))
[(1, 2, 3, 4), (1, 2, 4, 3), (1, 3, 2, 4), (1, 3, 4, 2), (1, 4, 2, 3), (1, 4, 3, 2), (2, 1, 3, 4), (2, 1, 4, 3), (2, 3, 1, 4), (2, 3, 4, 1), (2, 4, 1, 3), (2, 4, 3, 1), (3, 1, 2, 4), (3, 1, 4, 2), (3, 2, 1, 4), (3, 2, 4, 1), (3, 4, 1, 2), (3, 4, 2, 1), (4, 1, 2, 3), (4, 1, 3, 2), (4, 2, 1, 3), (4, 2, 3, 1), (4, 3, 1, 2), (4, 3, 2, 1)]
>>> x = itertools.permutations([1,2,3,4], 4)
>>> next(x)
(1, 2, 3, 4)
>>> next(x)
(1, 2, 4, 3)
>>> next(x)
(1, 3, 2, 4)
>>> next(x)
(1, 3, 4, 2)
>>> x = itertools.combinations([1,2,3,4], 4)
>>> list(x)
[(1, 2, 3, 4)]
>>> list(itertools.combinations([1,2,3,4,5], 3))
[(1, 2, 3), (1, 2, 4), (1, 2, 5), (1, 3, 4), (1, 3, 5), (1, 4, 5), (2, 3, 4), (2, 3, 5), (2, 4, 5), (3, 4, 5)]
10、accumulate()
>>> x = [1, 2, 3, 4, 5]
>>> itertools.accumulate(x)
<itertools.accumulate object at 0x0000000003181F08>
>>> list(itertools.accumulate(x))
[1, 3, 6, 10, 15]
>>> def sub(a, b):
return b-a
#后项减前项，即时生效
>>> list(itertools.accumulate(x, sub))[1, 1, 2, 2, 3]
>>> list(itertools.accumulate(x, lambda a,b: a*b))[1, 2, 6, 24, 120]
11、takewhile()、dropwhile()

>>> x = list(range(20))
>>> random.shuffle(x)
>>> x
[17, 3, 0, 13, 1, 4, 11, 9, 14, 16, 15, 18, 6, 7, 8, 19, 10, 5, 2, 12]
>>> list(itertools.takewhile(lambda x: x<18, x))
[17, 3, 0, 13, 1, 4, 11, 9, 14, 16, 15]
>>> list(itertools.takewhile(lambda x: x<19, x))
[17, 3, 0, 13, 1, 4, 11, 9, 14, 16, 15, 18, 6, 7, 8]
>>> list(itertools.dropwhile(lambda x: x<19, x))
[19, 10, 5, 2, 12]
>>> list(itertools.dropwhile(lambda x: x<18, x))
[18, 6, 7, 8, 19, 10, 5, 2, 12]
>>> list(itertools.dropwhile(lambda x: x<16, x))

[17, 3, 0, 13, 1, 4, 11, 9, 14, 16, 15, 18, 6, 7, 8, 19, 10, 5, 2, 12]

12、startmap()

功能说明：func(*seq[0]), func(*seq[1]), ...

>>> x = [(2, 5), (3, 2), (10, 3)]
>>> itertools.starmap(pow, x)
<itertools.starmap object at 0x0000000003187EB8>
>>> list(itertools.starmap(pow, x))
[32, 9, 1000]