Python: How to Compare 2 Lists (3 Approaches)

Comparing 2 lists in Python refers to determining whether the lists are equal or have any differences. Equality between lists is typically defined as having the same elements in the same order. However, in some specific use cases, 2 lists can be considered equal if they have the same elements regardless of the order.

Using the == operator (strict comparison)

This approach simply uses the == operator to compare 2 lists element-wise and returns True if they have the same length and the same elements in the same order and False otherwise. It also works for any type of element, even if they are not hashable or mutable.

Example:

list_a = ['a', 'b', 'c', [1, 2, 3], {'sling': 'academy'}]
list_b = ['a', 'b', 'c', [1, 2, 3], {'sling': 'academy'}]
list_c = ['a', 'b', 'c', [1, 2, 3, 4], {'sling': 'academy'}]

# compare list_a and list_b
if list_a == list_b:
    print('list_a and list_b are equal')
else:
    print('list_a and list_b are not equal')

# compare list_a and list_c
if list_a == list_c:
    print('list_a and list_c are equal')
else:
    print('list_a and list_c are not equal')

Output:

list_a and list_b are equal
list_a and list_c are not equal

Using the sorted() function and the == operator (loose comparison)

In case you want to check for equality regardless of the original order of the elements in the lists, this is the go-to solution. The main idea here is to use the sorted() function to sort both lists and then uses the == operator to compare them element-wise.

Example:

# Define 2 lists
list1 = [1, 2, 3, 4, 5]
list2 = [5, 4, 3, 2, 1]

# Sort both lists and compare them using the equality operator
result = sorted(list1) == sorted(list2)

# Print the result
print(result)

Output:

True

There is an important point you should be aware of. That is a limitation of the sorted() function. It can only sort elements that are comparable, which means they have a defined order and can be compared using the < operator. If you want to sort a list that contains different types of elements, you may need to use a custom key or comparator function that defines how to compare them. For example, you can use the str() function to convert every element into a string and then sort them lexicographically:

# Define 2 lists
list_a = ['a', 'b', 'c', [1, 2, 3], {'sling': 'academy'}]
list_b = [{'sling': 'academy'}, 'c', 'b' ,'a', [1, 2, 3], ]

# Sort both lists and compare them using the equality operator
result = sorted(list_a, key=str) == sorted(list_b, key=str)

# Print the result
print(result)

Output:

True

Using the all() and zip() functions (flexible comparison)

This approach uses the all() function and the zip() function to compare 2 lists element-wise. It returns True if they have the same length and every pair of corresponding elements are equal, and False otherwise.

Example:

list_a = ['a', 'b', 'c', [1, 2, 3], {'sling': 'academy'}]
list_b = ['a', 'b', 'c', [1, 2, 3], {'sling': 'academy'}]

# Use zip() and all() to compare the lists element-wise
result = all(x == y for x, y in zip(list_a, list_b))

# Print the result
print(result)

Output:

True

This approach is more verbose than the first approach, but it provides flexibility to define custom comparison logic. Short circuits if a mismatch is found.