Repeat counter when index ends

Question

Simple question - I want a loop that counts up and returns to 0 when it reaches a certain number.

Tried something like:

while i < 7:
    i += 1
    if i == 7
        i -= 1   #(or change i in any other way - you get the idea)

My Python actually crashed when I tried the above.

EDIT: Yes, the if condition is never met - it still crashes when I change it to if i == 6 though.

What do you mean by return? Directly return to 0 or decrement to zero? — Sam Chats, May 03 '18 at 15:21
[`for i in itertools.cycle(range(7)):`](https://docs.python.org/3/library/itertools.html#itertools.cycle)? — jonrsharpe, May 03 '18 at 15:22
it doesnt really matter if its decrementing or returning - i just cant find a way to change a variable if a while loop ends — Flying Thunder, May 03 '18 at 15:23
@jordanm { while i < 7: i += 1 return 0 } gives me a syntax error ("'return' outside function") — Flying Thunder, May 03 '18 at 15:25
If you want to re-run the loop multiple times you have to put it in a loop. Or write it in such a way that it never ends in the first place. — Aran-Fey, May 03 '18 at 15:27
With the colon, the code looks fine. You are going to have to be more specific about the error you are receiving. @jonrsharpe's suggestion would be the preferred way to write this, though. — chepner, May 03 '18 at 15:28
Why not leave the IF out and just st set i=0 after loop exits? — Scott Hunter, May 03 '18 at 15:30
the crash is not the issue here - i just want the counter to end at the maximum array lenght and then go back to 0. — Flying Thunder, May 03 '18 at 15:30
Do you want 1,2,3,4,5,6,7,6,5,4,... or 1,2,3,4,5,6,7,1,2,3,... ? — tobias_k, May 03 '18 at 15:37
it really doesnt matter as i said - i just want to generally know HOW to any of this, so an example on any of those two would do — Flying Thunder, May 03 '18 at 15:38
Well, if it does not matter, then either you really just have a typo (missing `:`) or the question is way too broad. — tobias_k, May 03 '18 at 15:38

score 1 · Accepted Answer · answered May 03 '18 at 15:36

1

while i < 7:
      i += 1
      if i == 7:
         i = 0

The problem is the i-=1 line. Your code works as i counts up to 6, but when it reaches 6, it is incremented to 7, and then subtracted down to 6 again. Your current sequence is 0,1,2,3,4,5,6,6,6,6,...

answered May 03 '18 at 15:36

SawyerWelden

100
1
9

still crashes though :/ – Flying Thunder May 03 '18 at 15:37
You haven't specified a reason for the program to stop, so it should loop infinitely. You need an exit condition. – SawyerWelden May 03 '18 at 15:42
i thought that the above "for" loop i used makes it finite - i am using the turtle module and want to change the color after each square until it drew 36 squares – Flying Thunder May 03 '18 at 15:46

Lorenzo Vincenzi · Answer 2 · 2018-05-03T15:41:01.507

0

If you want to count up to 7 then count down to 0 here is what you can try:

i = 0
add = True
while True:
    if add:
        i += 1
    else:
        i -= 1

    if i in [0, 7]:
        add = not add

edited May 03 '18 at 15:41

answered May 03 '18 at 15:34

Lorenzo Vincenzi

1,153
1
9
26

tells me that "name 'true' is not defined" – Flying Thunder May 03 '18 at 15:36
Sorry, the booleans value for python are "True" and "False". I'll edit the answer and improve the code quality – Lorenzo Vincenzi May 03 '18 at 15:38
ah, totally forgot that its case sensitive – Flying Thunder May 03 '18 at 15:39
You could also try something like `if i in (0, 7): increment *= -1` – tobias_k May 03 '18 at 15:40
still crashes. this is a tough one – Flying Thunder May 03 '18 at 15:42
@FlyingThunder No, it is not. It is just _very_ unclear what "crashes" means. I assume that it does not actually freeze your computer or similar. Does the program terminate with an exception? If so, _which exception_? – tobias_k May 03 '18 at 15:43
1

Maybe because this is an inifity loop. You should avoid it with a "End controll" – Lorenzo Vincenzi May 03 '18 at 15:44
Python not responding (Backend terminated (returncode: 3489660927)) – Flying Thunder May 03 '18 at 15:44
instead of "while True" use a counter to stop the iteration and increment its value into "if i in [0,7]" statement – Lorenzo Vincenzi May 03 '18 at 15:48

score 0 · Answer 3 · answered May 03 '18 at 15:49

0

This is your corrected code,

i = 0
while i < 7:
    i += 1
    if i == 6:
           i = 0

It reaches 0 on reaching 6. Lot's of syntax Error fixed.

answered May 03 '18 at 15:49

Nikhil.Nixel

555
2
11
25

the moment i added this python started crashing again – Flying Thunder May 03 '18 at 17:26
Python not responding (Backend terminated (returncode: 3489660927)) – Flying Thunder May 04 '18 at 06:52
@FlyingThunder Go to this link, https://stackoverflow.com/questions/285289/exit-codes-in-python – Nikhil.Nixel May 04 '18 at 06:57

Repeat counter when index ends

3 Answers3