Infinite for loops possible in Python?

Question

Is it possible to get an infinite loop in for loop?

My guess is that there can be an infinite for loop in Python. I\'d like to know this for future refe

Answer 1

Using itertools.count:

import itertools
for i in itertools.count():
    pass

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 but not infinity
    pass

Another way can be

def to_infinity():
    index=0
    while 1:
        yield index
        index += 1

for i in to_infinity():
    pass

Answer 2

The quintessential example of an infinite loop in Python is:

while True:
    pass

To apply this to a for loop, use a generator (simplest form):

def infinity():
    while True:
        yield

This can be used as follows:

for _ in infinity():
    pass

Answer 3

n = 0
li = [0]
for i in li:
    n += 1
    li.append(n)
    print(li)

In the above code, we iterate over the list (li).

• So in the 1st iteration, i = 0 and the code in for block will run, that is li will have a new item (n+1) at index 1 in this iteration so our list becomes [ 0, 1 ]
• Now in 2nd iteration, i = 1 and new item is appended to the li (n+1), so the li becomes [0, 1, 2]
• In 3rd iteration, i = 2, n+1 will be appended again to the li, so the li becomes [ 0, 1, 2, 3 ]

This will keep on going as in each iteration the size of list is increasing.

Answer 4

Why not try itertools.count?

import itertools
for i in itertools.count():
    print i

which would just start printing numbers from 0 to ...

Try it out.

**I realize I'm a couple of years late but it might help someone else :)

Answer 5

While there have been many answers with nice examples of how an infinite for loop can be done, none have answered why (it wasn't asked, though, but still...)

A for loop in Python is syntactic sugar for handling the iterator object of an iterable an its methods. For example, this is your typical for loop:

for element in iterable:
    foo(element)

And this is what's sorta happening behind the scenes:

iterator = iterable.__iter__()
try:
    while True:
        element = iterator.next()
        foo(element)
except StopIteration:
    pass

An iterator object has to have, as it can be seen, anextmethod that returns an element and advances once (if it can, or else it raises a StopIteration exception).

So every iterable object of which iterator'snextmethod does never raise said exception has an infinite for loop. For example:

class InfLoopIter(object):
    def __iter__(self):
        return self # an iterator object must always have this
    def next(self):
        return None

class InfLoop(object):
    def __iter__(self):
        return InfLoopIter()

for i in InfLoop():
    print "Hello World!" # infinite loop yay!

Answer 6

my_list = range(10)

for i in my_list:
    print ("hello python!!")
    my_list.append(i)