Python | Check if two lists are identical

Last Updated : 24 Nov, 2018

This article deals with the task of ways to check if two unordered list contains exact similar elements in exact similar position, i.e to check if two lists are exactly equal. This is quite a useful utility and can be used in day-day programming.

Method 1 : Using list.sort() and == operator
sort() coupled with == operator can achieve this task. We first sort the list, so that if both the lists are identical, then they have elements at the same position. But this doesn’t take into account the ordering of elements in list.

# Python 3 code to demonstrate 
# check if list are identical
# using sort() + == operator
  
# initializing lists 
test_list1 = [1, 2, 4, 3, 5]
test_list2 = [1, 2, 4, 3, 5]
  
# printing lists
print ("The first list is : " + str(test_list1))
print ("The second list is : " + str(test_list2))
  
# sorting both the lists
test_list1.sort()
test_list2.sort()
  
# using == to check if 
# lists are equal
if test_list1 == test_list2:
    print ("The lists are identical")
else :
    print ("The lists are not identical")

Output :

The first list is : [1, 2, 4, 3, 5]
The second list is : [1, 2, 4, 3, 5]
The lists are identical

Method 2 : Using collections.Counter()
Using Counter(), we usually are able to get frequency of each element in list, checking for it, for both the list, we can check if two lists are identical or not. But this method also ignores the ordering of the elements in the list and only takes into account the frequency of elements.

# Python 3 code to demonstrate 
# check if list are identical
# using collections.Counter()
import collections
  
# initializing lists 
test_list1 = [1, 2, 4, 3, 5]
test_list2 = [1, 2, 4, 3, 5]
  
# printing lists
print ("The first list is : " + str(test_list1))
print ("The second list is : " + str(test_list2))
  
# using collections.Counter() to check if 
# lists are equal
if collections.Counter(test_list1) == collections.Counter(test_list2):
    print ("The lists are identical")
else :
    print ("The lists are not identical")

Output :

The first list is : [1, 2, 4, 3, 5]
The second list is : [1, 2, 4, 3, 5]
The lists are identical

Method 3 : Using sum() + zip() + len()
Using sum() + zip(), we can get sum of one of the list as summation of 1 if both the index in two lists have equal elements, and then compare that number with size of other list. This also requires first to check if two lists are equal before this computation. It also checks for the order.

# Python 3 code to demonstrate 
# check if list are identical
# using sum() + zip() + len()
  
# initializing lists 
test_list1 = [1, 2, 4, 3, 5]
test_list2 = [1, 2, 4, 3, 5]
  
# printing lists
print ("The first list is : " + str(test_list1))
print ("The second list is : " + str(test_list2))
  
# using sum() + zip() + len() to check if 
# lists are equal
if len(test_list1)== len(test_list2) and len(test_list1) == sum([1 for i, j in zip(test_list1, test_list2) if i == j]):
    print ("The lists are identical")
else :
    print ("The lists are not identical")

Output :

The first list is : [1, 2, 4, 3, 5]
The second list is : [1, 2, 4, 3, 5]
The lists are identical

Method 4 : Using reduce() + map()
Carefully coupling power of map() to hash values and utility of reduce(), we can achieve this task of checking for equality of two lists to be identical. This also takes into account the ordering of the list.

# Python 3 code to demonstrate 
# check if list are identical
# using map() + reduce()
import functools
  
# initializing lists 
test_list1 = [1, 2, 4, 3, 5]
test_list2 = [1, 2, 4, 3, 5]
  
# printing lists
print ("The first list is : " + str(test_list1))
print ("The second list is : " + str(test_list2))
  
# using map() + reduce() to check if 
# lists are equal
if functools.reduce(lambda i, j : i and j, map(lambda m, k: m == k, test_list1, test_list2), True) : 
    print ("The lists are identical")
else :
    print ("The lists are not identical")

Output :

The first list is : [1, 2, 4, 3, 5]
The second list is : [1, 2, 4, 3, 5]
The lists are identical

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