How to find list intersection?

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

actual output: [1,3,5,6] expected output: [1,3,5]

How can we achieve a boolean AND operation (list intersection) on two lists?

Solution 1:

If order is not important and you don't need to worry about duplicates then you can use set intersection:

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

Solution 2:

Using list comprehensions is a pretty obvious one for me. Not sure about performance, but at least things stay lists.

[x for x in a if x in b]

Or "all the x values that are in A, if the X value is in B".

Solution 3:

If you convert the larger of the two lists into a set, you can get the intersection of that set with any iterable using intersection():

a = [1,2,3,4,5]
b = [1,3,5,6]
set(a).intersection(b)