Python - Join Lists

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In Python, List is classified as a sequence type object. It is a collection of items, which may be of different data types, with each item having a positional index starting with 0. You can use different ways to join two Python lists.

All the sequence type objects support concatenation operator (+), with which two lists can be joined.

Example

L1 = [10,20,30,40]
L2 = ['one', 'two', 'three', 'four']
L3 = L1+L2
print ("Joined list:", L3)

It will produce the following output −

Joined list: [10, 20, 30, 40, 'one', 'two', 'three', 'four']

Join Python Lists Using Augmented Concatenation Operator

You can also use the augmented concatenation operator with "+=" symbol to append L2 to L1

Example

L1 = [10,20,30,40]
L2 = ['one', 'two', 'three', 'four']
L1+=L2
print ("Joined list:", L1)

The same result can be obtained by using the extend() method. Here, we need to extend L1 so as to add elements from L2 in it.

L1 = [10,20,30,40]
L2 = ['one', 'two', 'three', 'four']
L1.extend(L2)
print ("Joined list:", L1)

Join Python Lists by Appending Items

To add items from one list to another, a classical iterative solution also works. Traverse items of second list with a for loop, and append each item in the first.

Example

L1 = [10,20,30,40]
L2 = ['one', 'two', 'three', 'four']

for x in L2:
   L1.append(x)
   
print ("Joined list:", L1)

Join Python Lists using List Comprehension

A slightly complex approach for merging two lists is using list comprehension, as following code shows −

Example

L1 = [10,20,30,40]
L2 = ['one', 'two', 'three', 'four']
L3 = [y for x in [L1, L2] for y in x]
print ("Joined list:", L3)