In Python what's some other ways to write a if x==1 or x==5 or x==10...?

Question

I often end up writing code like

if x == 1 or x == 5 or x == 10 or x == 22 :
    pass

In English it seems redundant to keep repeating x, is there an easier or shorter way to write out an if-statement like that?

Maybe checking of existence of x's value in a tuple ( 1, 5, 10, 22, ) or something?

Answer 1

Yes, you are right - either in a tuple or (if this check is made repeatedly) in a set.

So either do

if x in (1, 5, 10, 22):
    pass

or, if you do this check often and the number of values is large enough,

myset = set((1, 5, 10, 22))

[...]

if x in myset:
    pass

The myset stuff is the more useful, the more values you want to check. 4 values are quite few, so you can keep it simple. 400 values and you should use the set...

Another aspect, as pointed out by Marcin, is the necessary hashing for lookup in the set which may be more expensive than linearly searching a list or tuple for the wanted value.

Answer 2

You can use in with a collection:

if x in [1, 5, 10, 22]:
     # etc...

if x in {1, 5, 10, 22}:  # New syntax for creating sets  
     # etc...

Note that this will create a new list every time the line executes. If efficiency is a concern, create the collection only once and reuse it.

Answer 3

If you need good performance and are going to repeat the same comparison several times, use a set:

s = frozenset([1, 5, 10, 22]) # at the beginning

if x in s: # in your code
    pass