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pythonloopsrepeat
phos456
phos456

Reputation: 19

How to repeat a for loop

I have got one problem with Python. I'm trying to repeat a for loop more than once. I have a condition inside the loop, and if the condition is true, the loop should start again. I need the solution only with one for loop. For example:

for i in range (10):
    if i==4:
        i=0
    print(i)

Unfortunately this doesn't work.

The output should be: 0 1 2 3 0 1 2 3 0 1 2 3...

Upvotes: 0

Views: 10298

Answers (3)

Kasravnd
Kasravnd

Reputation: 107347

Converting the through away variable i to 0 at the bottom level of the loop doesn't mean that in next iteration your variable shall be 0, because in each iteration python reassigned it automatically.

As a more pythonic way for such tasks you can use itertools.cycle

>>> def range_printer(r,N): # r is the length of your range and N is the number of sequence printing 
...     a=cycle(range(r))
...     for i in range(N*r):
...         print next(a)
... 
>>> range_printer(4,3)
0
1
2
3
0
1
2
3
0
1
2
3

Or you can use yield to return a generator :

>>> def range_printer(r,N):
...     a=cycle(range(r))
...     for i in range(N*r):
...         yield next(a)
... 
>>> list(range_printer(4,3))
[0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3]

Upvotes: 2

hiro protagonist
hiro protagonist

Reputation: 46921

a version using itertools.cycle:

from itertools import cycle

for i in cycle(range(4)):
    # put your logic that `break`s the cycle here
    print(i)

Upvotes: 2

Reut Sharabani
Reut Sharabani

Reputation: 31349

Writing to the loop's variable (i) inside the loop is always not a good idea (that includes all languages I'm familiar with).

Try using a while loop instead:

i = 0
while i < 10:
    i += 1
    if i == 4:
        i = 0

The same logic can be implemented with:

while True:
    for i in range(4):
        print(i)

Or using the modulo operator which is common when cycling:

i = 0
while True:
    print(i % 4)
    i += 1

Upvotes: 4

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