in list VS in tuple condition in python

Question

I want to know what are the best practices between using the in tuple and the in list conditions and know why, as the following scenario:

my_variable = 'A'
if my_variable in [2, 'A', None]:
    return True
elif my_variable in (2, 'A', None):
    return True

And if possible list the advantages/disadvantages of tuples/lists in this case.

Answer 1

list and tuple both have an O(n) time complexity for x in container checks.

However, set have an O(1) for this check (most of the time, the worst case scenario will have a worse time complexity due to hash collisions).

See these timings for a list, tuple and a set with 1 million elements:

from timeit import Timer

li = list (range(1, 1000000))
t =  tuple(range(1, 1000000))
s =  set  (range(1, 1000000))

def x_in_list():
    999999 in li

def x_in_tuple():
    999999 in t

def x_in_set():
    999999 in s

print(min(Timer(x_in_list).repeat(5, 5)))
print(min(Timer(x_in_tuple).repeat(5, 5)))
print(min(Timer(x_in_set).repeat(5, 5)))

Outputs

0.08769642199999961
0.09637485699999981
9.329999999252436e-07

Answer 2

The difference in runtime is negligible between List, Tuple, and Set if there are only 3 elements.

Pep8 style guide doesn't say anything about this as far as I know, so you can use whichever you prefer.

Something the other answers missed, as far as readability goes, is you can declare a set directly like this:

if my_variable in {2, 'A', None}:
    print(True)

Answer 3

A tuple is an immutable sequence, whereas a list is a mutable sequence, which means tuples can't be changes, but list can be.

If you don't want to modify the data structure you are checking in , use tuple , else use list, otherwise both behave the same.

my_variable = 'A'

if my_variable in [2, 'A', None]:
    print(True)
if my_variable in (2, 'A', None):
    print(True)

The output will be

True
True

Note that both list and tuple have O(n) time complexity to check, to get an average O(1) complexity, use a set.

if my_variable in set([2, 'A', None]):
    print(True)
#True