Python: how to find common values in three lists

Question

I try to find common list of values for three different lists:

a = [1,2,3,4]
b = [2,3,4,5]
c = [3,4,5,6]

of course naturally I try to use the and operator however that way I just get the value of last list in expression:

>> a and b and c
out: [3,4,5,6]

Is any short way to find the common values list:

[3,4]

Br

Answer 1

Use sets:

>>> a = [1, 2, 3, 4]
>>> b = [2, 3, 4, 5]
>>> c = [3, 4, 5, 6]
>>> set(a) & set(b) & set(c)
{3, 4}

Or as Jon suggested:

>>> set(a).intersection(b, c)
{3, 4}

Using sets has the benefit that you don’t need to repeatedly iterate the original lists. Each list is iterated once to create the sets, and then the sets are intersected.

The naive way to solve this using a filtered list comprehension as Geotob did will iterate lists b and c for each element of a, so for longer list, this will be a lot less efficient.