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Python – Append Missing elements from other List

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  • Last Updated : 02 Sep, 2020
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Given 2 lists, append elements missing from list 1 to list 2.

Input : test_list1 = [5, 6, 4, 8, 9, 1], test_list2 = [9, 8, 10]
Output : [5, 6, 4, 1, 9, 8, 10]
Explanation : 5, 6, 4, 1 added to list 2, in order.

Input : test_list1 = [5, 6, 4, 8, 9, 1], test_list2 = [9, 10]
Output : [5, 6, 4, 8, 1, 9, 10]
Explanation : 5, 6, 4, 8, 1 added to list 2, in order.

Method #1 : Using list comprehension

In this, we iterate list 1 to check for missing elements in list 2, then add these elements to list 2.

Python3




# Python3 code to demonstrate working of 
# Append Missing elements from other List
# Using list comprehension
  
# initializing list
test_list1 = [5, 6, 4, 8, 9, 1]
test_list2 = [9, 8, 7]
  
# printing original lists
print("The original list 1 is : " + str(test_list1))
print("The original list 2 is : " + str(test_list2))
  
# extracting elements from list 1 which are not in list 2
temp1 = [ele for ele in test_list1 if ele not in test_list2]
  
# constructing result 
res = temp1 + test_list2
  
# printing result 
print("The modified list 2 : " + str(res))

Output

The original list 1 is : [5, 6, 4, 8, 9, 1]
The original list 2 is : [9, 8, 7]
The modified list 2 : [5, 6, 4, 1, 9, 8, 7]

Method #2 : Using set() + “-” operator + extend()

In this, we check for elements of list 1 missing from list 2 using set() and – operator and extend() is used to join both the list to get desired result.

Python3




# Python3 code to demonstrate working of 
# Append Missing elements from other List
# Using set() + "-" operator + extend()
  
# initializing list
test_list1 = [5, 6, 4, 8, 9, 1]
test_list2 = [9, 8, 7]
  
# printing original lists
print("The original list 1 is : " + str(test_list1))
print("The original list 2 is : " + str(test_list2))
  
# finding missing words
rem_list = (set(test_list1) - set(test_list2))
  
# checking order
res = [ele for ele in test_list1 if ele in rem_list] 
  
# joining result
res.extend(test_list2)
  
# printing result 
print("The modified list 2 : " + str(res))

Output

The original list 1 is : [5, 6, 4, 8, 9, 1]
The original list 2 is : [9, 8, 7]
The modified list 2 : [5, 6, 4, 1, 9, 8, 7]

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