CODEWITHSUNDEEP
pythonlisttuplesconditional-statements
getName
getName

Reputation: 733

in list VS in tuple condition in python

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.

Upvotes: 3

Views: 668

Answers (3)

James Audretsch
James Audretsch

Reputation: 11

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)

Upvotes: 1

DeepSpace
DeepSpace

Reputation: 81664

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

Upvotes: 4

Devesh Kumar Singh
Devesh Kumar Singh

Reputation: 20500

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

Upvotes: -1

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