python中的itertools的使用详解

from itertools import count

"""
无穷的迭代器 count()
"""
c = count(0, 2)
v = next(c)
while v < 10:
  v = next(c)
  print(v, end=',')

"""
无穷迭代器 cycle()
"""
from itertools import cycle

c = cycle('ABCD')
for i in range(10):
  print(next(c), end=',')

"""
无穷迭代器 repeat()
"""
from itertools import repeat

r = repeat(1, 3)
for i in range(3):
  print(next(r), end=',')

"""
迭代器 accumulate()
"""
from itertools import accumulate

test_list = [i for i in range(1, 11)]
for i in accumulate(test_list): # 默认是operator.add
  print(i, end=',')
print()
for i in accumulate(test_list, lambda x, y: x * y): # operator.mul
  print(i, end=',')

"""
迭代器 chain()
"""
from itertools import chain

ch = chain([1, 2, 3], {4: 4, 5: 5}, {6, 7, 8}, (9,), [10, [11, 12]])
for i in ch:
  print(i)

"""
迭代器 chain.from_iterable()
"""
def gen_iterables():
  for i in range(10):
    yield range(i)

for i in chain.from_iterable(gen_iterables()):
  print(i)

"""
迭代器 compress
"""
from itertools import compress

print(list(compress(['A', 'B', 'C', 'D'], [0, 1, 1, 1])))

"""
迭代器 dropwhile()
"""
from itertools import dropwhile

l = [1, 7, 6, 3, 8, 2, 10]
print(list(dropwhile(lambda x: x < 3, l)))

from itertools import groupby

# 对字符串进行分组
for k, g in groupby('11111234567'):
  print(k, list(g))
d = {1: 1, 2: 2, 3: 2}
# 按照字典value来进行分组
for k, g in groupby(d, lambda x: d.get(x)):
  print(k, list(g))

from itertools import islice
print(list(islice('ABCDEFG', 2,3, None)))

from itertools import zip_longest

for x,y in zip_longest([1,2,3],[1,2]):
  print(x,y)
for x,y in zip([1,2,3],[1,2]):
  print(x,y)
 

“”"
排列组合迭代器 product 嵌套的for
“”"
from itertools import product
for i,j in product([1,2,3],[4,5]):
print(i,j

from itertools import permutations
print(list(permutations('123')))
 

from itertools import combinations
print(list(combinations([1,2,3],2)))