Infinite for loop in Python like C++

Question

In C++ we can write an infinite for loop like for(;;). Is here any syntax like this to write an infinite for loop in Python?

Note : I know that if I write for i in range(a_very_big_value) then it may run infinity. I am searching a simple syntax like C++ or any other tricks to write infinite for loop in Python.

Answer 1

Python's for statement is a "for-each" loop (sort of like range-for in C++11 and later), not a C-style "for-computation" loop.

But notice that in C, for (;;) does the same thing as while (1). And Python's while loop is basically the same as C's with a few extra bells and whistles. And, in fact, the idiomatic way to loop forever is:¹

while True:

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If you really do want to write a for loop that goes forever, you need an iterable of infinite length. You can grab one out of the standard library:²

for _ in itertools.count():

… or write one yourself:

def forever():
    while True:
        yield None

for _ in forever():

But again, this isn't really that similar to for (;;), because it's a for-each loop.

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_{1. while 1: used to be a common alternative. It's faster in older versions of Python, although not in current ones, and occasionally that mattered.}

_{2. Of course the point of count isn't just going on forever, it's counting up numbers forever. For example, if enumerate didn't exist, you could write it as zip(itertools.count(), it).}

Answer 2

Yes, it is possible.

With a while loop:

while True:
   ...

With a for loop (just for kicks):

from itertools import cycle    
for _ in cycle(range(1)):
    ...

The cycle returns 1 indefinitely.

In either case, it's up to you to implement your loop logic in such a way that you terminate eventually. And lastly, if you want to implement an execute-until-___ loop, you should stick to while True, because that's the idiomatic way of doing it.

Answer 3

I found the answer from here and here

Using itertools.count:

import itertools
for i in itertools.count():
    if there_is_a_reason_to_break(i):
        break

In Python2 xrange() is limited to sys.maxint, which may be enough for most practical purposes:

import sys
for i in xrange(sys.maxint):
    if there_is_a_reason_to_break(i):
        break

In Python3, range() can go much higher, though not to infinity:

import sys
for i in range(sys.maxsize**10):  # you could go even higher if you really want
    if there_is_a_reason_to_break(i):
        break

So it's probably best to use count()

---

It is also possible to achieve this by mutating the list you're iterating on, for example:

l = [1]
for x in l:
    l.append(x + 1)
    print(x)

Answer 4

Yes, here you are:

for i in __import__("itertools").count():
    pass

The infinite iterator part was taken from this answer. If you really think about it though, a while loop looks way better.

while True:
    pass

Answer 5

You can use:

while True:
    # Do stuff here

Answer 6

for _ in iter(str, "forever"):
...     pass

This may help. Because the iter() function creates an iterator that will call str() with no arguments for each call to its next() method[ This returns an empty string ]; if the value returned by str() is equal to the string "forever"(WHICH WILL NEVER HAPPEN AS "" != "forever"), StopIteration will be raised thus breaking the loop, otherwise the loop will continue running and this is the case for our loop.

REF: https://docs.python.org/3/library/functions.html?highlight=iter#iter