abbreviating a double comparison in python

Question

Is there a way to abbreviate a comparison statement in python so that I don't have to write the whole thing out again? For example, instead of :

a=3
if a==3 or a==2:
    print "hello world"

could I do something like: if a==(3 or 2): print "hello world"

I know the above example won't work but is there another way i can achieve the desired effect?

score 14 · Answer 1 · answered May 16 '12 at 19:56

14

if a in (2, 3):
  print "hello world"

answered May 16 '12 at 19:56

NPE

Re your edit: is it preferable to use a tuple instead of a list? – Levon May 16 '12 at 19:57
4

@Levon: I don't have a strong preference either way, but to my eye a tuple looks slightly more natural here. – NPE May 16 '12 at 19:58
ok, thanks .. I know sometimes there are subtle differences, just wanted to make sure I didn't miss anything as I generally use lists for this. – Levon May 16 '12 at 19:59
4

It's just a matter of style, but there is definitely a general principle that justifies preferring a tuple to a list: use more restricted tools when you can get away with it, and the powerful ones only when they're needed - that way, the reader of the code won't be distracted by thinking of functionality that won't actually be used. Here, use a tuple because you aren't going to use the list-specific functionality of modification in-place. – Karl Knechtel May 16 '12 at 20:01
While it's probably unlikely that this would be a case where it matters, tuples are quite a bit faster to create than lists in Python: http://stackoverflow.com/questions/68630/are-tuples-more-efficient-than-lists-in-python – Wilduck May 16 '12 at 20:17

robert · Answer 2 · 2012-05-16T20:10:39.587

14

Possible solutions, depending on what exactly you want:

edited May 16 '12 at 20:10

answered May 16 '12 at 19:57

robert

Is there a benefit to using `xrange` instead of `range` in this case? I'm so glad Python 3 did away with `xrange`. – Mark Ransom May 16 '12 at 20:04
@MarkRansom In this case it probably doesn't matter. – robert May 16 '12 at 20:07
@robert +1but if it doesn't matter it would be best to use range for py3x compatibility. – jamylak May 16 '12 at 21:58
2

but range has to put a list in memory with all the numbers so `3 in range(9999999999999)` raises an exception but `3 in xrange(9999999999999)` works – m0etaz Nov 28 '18 at 10:32

score 13 · Answer 3 · answered May 16 '12 at 20:11

13

See Python 3.2 Optimizations regarding the reason for the answer below.

a = 3
if a in {2, 3}:
    print('Hello, world!')

answered May 16 '12 at 20:11

Noctis Skytower

3 Answers3