How can I using yield list element infinitely

Question

I have directory list and this element should be returned at one at a time

so I coded like below:

def gen():
    list = ["dir_1", "dir_2", ..., "dir_n"]
    for i in list:
        yield i

But, I wanna get directory over and over again, e.g dir_1, dir_2, … ,dir_n, dir_1, dir_2… like that.

How should I do?

Asked By: YeongHwa Jin

||

Source

Answer 1

You can use itertools.cycle for exactly what you describe:

from itertools import cycle
def gen():
    lst = ["dir_1", "dir_2", "dir_n"]
    for i in cycle(lst):
        yield i

so that:

i = gen()
for _ in range(5):
    print(next(i))

outputs:

dir_1
dir_2
dir_n
dir_1
dir_2

Answered By: blhsing

Answer 2

This is a solution by the means of While loop.

def gen():
    while True:
        mylist = ["dir_1", "dir_2"]
        for i in mylist:
            yield i

Answered By: Chun Kit Yeung

Answer 3

You can use cycle, no need for another generator just call cycle on an iterator and it will cycle forever

from itertools import cycle

for dir in cycle(["dir_1", "dir_2", "dir_n"]):
   do stuff ...
   if some_reason:
     break

Answered By: geckos

Answer 4

The following solution should be faster and more efficient:

def gen(lst):
    yield from lst
    yield from gen(lst)

Usage:

>>> g = gen(['a','b','c'])

>>> for x in g:
>>>     do something...
>>>     if some_reason:
>>>         break

>>> [next(g) for _ in range(7)]
['a', 'b', 'c', 'a', 'b', 'c', 'a']

Alternatively, if you want a limit to the cycling generator, you can use the following version which allows you to set (optionally) the total length of the output sequence:

def gen(lst,limit=None):
    if type(limit) == int:
        g = gen(lst)
        for _ in range(limit):
            yield next(g)
        return
    yield from lst
    yield from gen(lst,limit)

Usage:

>>> g = gen(['a','b','c'], limit=7))

>>> for x in g:
>>>     do something (for 7 times)...

>>> list(g)
['a', 'b', 'c', 'a', 'b', 'c', 'a']

N.B. If the limit you set is greater than Python recursion capabilities (usually 1000 recursions) you can improve such capabilities through the following code:

>>> import sys
>>> sys.setrecursionlimit(some_greater_limit)

Answered By: mmj

How can I using yield list element infinitely

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