Question

我正在使用Python 无限迭代列表，重复列表中的每个元素多次。例如，给出列表：

l = [1, 2, 3, 4]

我想输出每个元素两次，然后重复循环：

1, 1, 2, 2, 3, 3, 4, 4, 1, 1, 2, 2 ...

我知道从哪里开始：

def cycle(iterable):
  if not hasattr(cycle, 'state'):
    cycle.state = itertools.cycle(iterable)
  return cycle.next()

 >>> l = [1, 2, 3, 4]
 >>> cycle(l)
 1
 >>> cycle(l)
 2
 >>> cycle(l)
 3
 >>> cycle(l)
 4
 >>> cycle(l)
 1

但我如何重复每个元素？

修改

澄清这应该无限迭代。我也用过两次重复元素作为最短的例子 - 我真的想重复每个元素n次。

更新

您的解决方案会引导我找到我想要的东西：

>>> import itertools
>>> def ncycle(iterable, n):
...   for item in itertools.cycle(iterable):
...     for i in range(n):
...       yield item
>>> a = ncycle([1,2], 2)
>>> a.next()
1
>>> a.next()
1
>>> a.next()
2
>>> a.next()
2
>>> a.next()
1
>>> a.next()
1
>>> a.next()
2
>>> a.next()
2

感谢您的快速解答！

Answer 1

这个怎么样：

import itertools

def bicycle(iterable, repeat=1):
    for item in itertools.cycle(iterable):
        for _ in xrange(repeat):
            yield item

c = bicycle([1,2,3,4], 2)
print [c.next() for _ in xrange(10)]

编辑：合并bishanty's重复计数参数和Adam Rosenfield's list comprehension。

Answer 2

你可以很容易地用发电机做到这一点：

def cycle(iterable):
    while True:
        for item in iterable:
            yield item
            yield item

x=[1,2,3]
c=cycle(x)

print [c.next() for i in range(10)]  // prints out [1,1,2,2,3,3,1,1,2,2]

Answer 3

itertools.chain.from_iterable(itertools.repeat(item, repeat) for item in itertools.cycle(l))

Answer 4

解决方案应该是

iterable = [1, 2, 3, 4]
n = 2

while (True):
  for elem in iterable:
    for dummy in range(n):
      print elem # or call function, or whatever

编辑：添加'While（True）'无限期迭代。

Answer 5

import itertools as it

def ncycle(iterable, n=1):
    if n == 1:
        return it.cycle(iterable)
    return it.cycle(it.chain(*it.izip(*([iterable]*n))))

Answer 6

我是这样做的：

from itertools import cycle, repeat, chain
flatten = chain.from_iterable # better name

def ncycle(xs, n):
    return flatten(repeat(x, n) for x in cycle(xs))

# example
for n,x in enumerate(ncycle('abcd', 2)):
    print(x, end=" ")
    if n > 9:
        print("")
        break
# output: a a b b c c d d a a b

Answer 7

[ "%d, %d" % (i, i) for i in [1, 2, 3, 4] * 4]

最后4个循环次数。

如何迭代重复Python中每个元素的列表

7 个答案: