How do I make an infinite for loop in Python (without using a while loop)?

Question

Is there way to write an infinite for loop in Python?

for t in range(0,10):
    if(t == 9): t= 0 # will this set t to 0 and launch infinite loop? No!
    print(t)

Generally speaking, is there way to write infinite pythonic for loop like in java without using a while loop?

@joelgoldstick, i m making slides for high schools about python, i made one about while infinite loop and got curious - is there way to do infinite loop in python, so that's why asking — ERJAN, Apr 29 '16 at 11:12
I 'm curious to why `for i in range(0, 1, -1) : print("Hello")` too doesn't work? — Vishesh Mangla, Jul 18 '20 at 18:11

snakecharmerb · Answer 1 · 2018-08-23T19:33:28.697

8

The itertools.repeat function will return an object endlessly, so you could loop over that:

import itertools
for x in itertools.repeat(1):
    pass

edited Aug 23 '18 at 19:33

answered Apr 29 '16 at 11:10

snakecharmerb

score 7 · Answer 2 · answered Apr 29 '16 at 11:12

7

To iterate over an iterable over and over again, you would use itertools.cycle:

from itertools import cycle
for t in cycle(range(0, 4)):
    print(t)

This will print the following output:

answered Apr 29 '16 at 11:12

Byte Commander

mvelay · Answer 3 · 2016-04-29T11:25:35.133

4

You should create your own infinite generator with cycle

from itertools import cycle

gen = cycle([0])

for elt in gen:
    # do stuff

or basically use itertools.count():

for elt in itertools.count():
    # do stuff

edited Apr 29 '16 at 11:25

answered Apr 29 '16 at 11:08

mvelay

What do you mean by `cycle(_)` (the underscore)? – Byte Commander Apr 29 '16 at 11:16
it's a convention for throwaway variables – mvelay Apr 29 '16 at 11:18
Yes, but it is not assigned in your example. Running that, you will get a `NameError: name '_' is not defined`. – Byte Commander Apr 29 '16 at 11:21
By default, it is assigned to '' in my ipython console... You're right thx ! – mvelay Apr 29 '16 at 11:24
2

In interactive consoles it has a different meaning usually, there it represents the result of the last operation. – Byte Commander Apr 29 '16 at 11:27
sure, but at first launch it is set to '', probably somewhere in my ipython config file... – mvelay Apr 29 '16 at 11:28
And for just repeating the same value over and over again, you use `repeat`. You only use `cycle` when you want to repeatedly iterate over an iterable object like a list. – Byte Commander Apr 29 '16 at 11:30

score -7 · Answer 4 · answered Apr 29 '16 at 11:07

-7

Just pass could help with forever true value.

while True:
    pass

answered Apr 29 '16 at 11:07

Vishal Yarabandi

4 Answers4