How to compare two lists in Python

In comparing lists, we are checking the data items of a list against equality with data items of another list. In this article, we will discuss different ways to compare two lists.

Method 1: Using list comprehension

l1 = [1, 6, 2, 7]
l2 = [7, 4, 1, 2, 3]
#r is the list containing elements that are not present in both lists
r = [i for i in l1 +l2 if i not in l1 or i not in l2]

if (r):
    print("Lists are not equal")
    print(r)
else:
    print("Lists are equal")

Output:

Lists are not equal
[6, 4, 3]

Method 2: Using sort() method and == operator

In this method, we are sorting the lists first. If the two lists are equal, then the elements would reside at the same index positions. == operator compares element by element.

l1 = [1, 6, 2, 7]
l2 = [7, 4, 1, 2, 3]
l3 = [6, 2, 1, 7]

l1.sort()
l2.sort()
l3.sort()

if l1==l2:
    print("Lists l1 and l2 are equal")
else:
    print("Lists l1 and l2 are not equal")

if l1==l3:
    print("Lists l1 and l3 are equal")
else:
    print("Lists l1 and l3 are not equal")

Output:

Lists l1 and l2 are not equal
Lists l1 and l3 are equal

Method 3: Using collection.counter method

This method can be used to compare lists efficiently. The counter() function counts the frequency of the items in a list and stores the data as a dictionary in the format <value>:<frequency>. If two lists have the exact same dictionary output, we can assume that the lists are the same.

import collections

l1 = [1, 6, 2, 7]
l2 = [7, 4, 1, 2, 3]
l3 = [6, 2, 1, 7]

if collections.Counter(l1) == collections.Counter(l2):
    print("Lists l1 and l2 are equal")
else:
    print("Lists l1 and l2 are not equal")

if collections.Counter(l1) == collections.Counter(l3):
    print("Lists l1 and l3 are equal")
else:
    print("Lists l1 and l3 are not equal")

Output:

Lists l1 and l2 are not equal
Lists l1 and l3 are equal