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Python | Insert list in another list

  • Difficulty Level : Basic
  • Last Updated : 26 Jan, 2019

The problem of inserting a number at any index is a quite common one. But sometimes we require to insert the whole list into another list. These kinds of problems occur in Machine Learning while playing with data. Let’s discuss certain ways in which this problem can be solved.

Method #1 : Using insert() + loop
In this method, we insert one element by 1 at a time using the insert function. This way we add all the list elements at the specified index in other list.




# Python3 code to demonstrate 
# to insert one list in another
# using insert() + loop
  
# initializing lists 
test_list = [4, 5, 6, 3, 9]
insert_list = [2, 3]
  
# initializing position
pos = 2
  
# printing original list
print ("The original list is : " + str(test_list))
  
# printing insert list 
print ("The list to be inserted is : " + str(insert_list))
  
# using insert() + loop
# to insert one list in another
for i in range(len(insert_list)):
    test_list.insert(i + pos, insert_list[i])
  
# printing result 
print ("The list after insertion is : " +  str(test_list))

Output :

The original list is : [4, 5, 6, 3, 9]
The list to be inserted is : [2, 3]
The list after insertion is : [4, 5, 2, 3, 6, 3, 9]

 
Method #2 : Using list slicing
This is the most pythonic and elegant way to perform this particular task. In this method, we just slice the list where we need to add the element and assign the list to be inserted.




# Python3 code to demonstrate 
# to insert one list in another
# using list slicing
  
# initializing lists 
test_list = [4, 5, 6, 3, 9]
insert_list = [2, 3]
  
# initializing position
pos = 2
  
# printing original list
print ("The original list is : " + str(test_list))
  
# printing insert list 
print ("The list to be inserted is : " + str(insert_list))
  
# using list slicing
# to insert one list in another
test_list[pos:pos] = insert_list
  
# printing result 
print ("The list after insertion is : " +  str(test_list))

Output :

The original list is : [4, 5, 6, 3, 9]
The list to be inserted is : [2, 3]
The list after insertion is : [4, 5, 2, 3, 6, 3, 9]

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