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.
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:
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.
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).
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.
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)
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
You can use:
while True:
# Do stuff here
for loop not while loop :(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
while loop, I am searching forfor loop.C++background, that's why I am searching for something likeC++. You can say it curiosity.forloop is than the C-style for loop.