How to count by twos with Python's 'range'

Question

So imagine I want to go over a loop from 0 to 100, but skipping the odd numbers (so going "two by two").

for x in range(0,100):
    if x%2 == 0:
        print x

This fixes it. But imagine I want to do so jumping two numbers? And what about three? Isn't there a way?

score 68 · Accepted Answer · edited Apr 02 '20 at 01:16

68

Use the step argument (the last, optional):

for x in range(0, 100, 2):
    print(x)

Note that if you actually want to keep the odd numbers, it becomes:

for x in range(1, 100, 2):
    print(x)

Range is a very powerful feature.

edited Apr 02 '20 at 01:16

cinemassacres

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answered Dec 28 '14 at 16:11

Jivan

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You've just edited it, but I guess `step=2` also worked. Am I wrong? – Dec 28 '14 at 16:12
@JuanRocamonde range() doesn't take keyword arguments, in fact – Jivan Dec 28 '14 at 16:13
Ok so that means it wouldn't. Thanks for your reply – Dec 28 '14 at 16:13
@JuanRocamonde Is that what you were asking for? – Jivan Dec 28 '14 at 16:15
@JuanRocamonde don't forget to accept the answer so that other users can identify it (only if you're actually happy with that) – Jivan Dec 28 '14 at 16:21
Yes once the timer lets me :) – Dec 28 '14 at 16:22
2

I think your answer might have a mistake, since `range(1, 100, 2)` starts iterating with `1` and thus skips the _even_ numbers, whereas `range(0, 100, 2)` starts iterating at `0` and thus skips the _odd_ numbers. – David Z Dec 28 '14 at 21:09
@DavidZ right! non-English speaker, I always confuse odd/even :) answer edited, thanks – Jivan Dec 28 '14 at 21:10

score 3 · Answer 2 · edited Dec 28 '14 at 23:39

(Applicable to Python <= 2.7.x only)

In some cases, if you don't want to allocate the memory to a list then you can simply use the xrange() function instead of the range() function. It will also produce the same results, but its implementation is a bit faster.

for x in xrange(0,100,2):
    print x,   #For printing in a line

>>> 0, 2, 4, ...., 98

Python 3 actually made range behave like xrange, which doesn't exist anymore.

score 3 · Answer 3 · edited Dec 28 '14 at 23:40

3

for i in range(0, 100, 2):
    print i

If you are using an IDE, it tells you syntax:

min, max, step(optional)

edited Dec 28 '14 at 23:40

Peter Mortensen

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answered Dec 28 '14 at 20:50

Secret Name

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Yep, but I wanted to say about IDE syntax help :P – Secret Name Dec 28 '14 at 20:53

How to count by twos with Python's 'range'

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