Moving back an iteration in a for loop

Question

So I want to do something like this:

for i in range(5):
    print(i);
    if(condition==true):
        i=i-1;

However, for whatever reason, even though I'm decrementing i, the loop doesn't seem to notice. Is there any way to repeat an iteration?

Answer 1

for loops in Python always go forward. If you want to be able to move backwards, you must use a different mechanism, such as while:

i = 0 while i < 5:     print(i)     if condition:         i=i-1     i += 1 

Or even better:

i = 0 while i < 5:     print(i)     if condition:         do_something()         # don't increment here, so we stay on the same value for i     else:         # only increment in the case where we're not "moving backwards"         i += 1 

Answer 2

Python loop using range are by-design to be different from C/C++/Java for-loops. For every iteration, the i is set the the next value of range(5), no matter what you do to i in between.

You could use a while-loop instead:

i = 0
while i<5:
    print i
    if condition:
        continue
    i+=1

But honestly: I'd step back and think again about your original problem. Probably you'll find a better solution as such loops are always error-prone. There's a reason why Python for-loops where designed to be different.