Merge Two Lists in Python

Merging Two Lists in Python

Merging lists means adding or concatenating one list with another. In simple words, it means joining two lists. We can use various ways to join two lists in Python. Let us discuss them below:

1. Using append() function

One simple and popular way to merge(join) two lists in Python is using the in-built append() method of python. The append() method in python adds a single item to the existing list. It doesn't return a new list of items. Instead, it modifies the original list by adding the item to the end of the list.

Code:

Output:

Explanation:

• In the above code, we declare two lists, ls1 and ls2.
• We iterate over ls2 and append its elements to ls1 using our python's append method.

2. Using the '+' Operator

This is the simplest way to merge two lists in Python. '+' operator is a multipurpose operator, which we can use for arithmetic calculations and for merging purposes, strings, lists, etc.

Code:

Output:

Explanation:

• We defined our lists ls1 and ls2
• Then, we merged them using the '+' operator in Python.
• The use of + operator adds the whole of one list behind the other list.

3. Using List Comprehension

We can merge two lists in Python using list comprehension as well. List comprehension offers a shorter and crisper syntax when we want to create a new list based on the values of an existing list. It may also be called an alternative to the loop method.

Code:

Output:

Explanation:

• In the above example, first, this line is executed for n in (num1,num2), which will return [[1, 2, 3], [4, 5, 6]].
• After that, we pick one element at a time from the above lists. Hence we do for x in n.
• Finally, we get our desired result by storing the value of x in the list: [x for n in (num1,num2) for x in n]

4. Using the extend() method

The extend() method adds all the elements of an iterable (list, tuple, string, etc.) to the end of the list. It updates the original list itself. Hence its return type is None. It can be used to merge two lists in Python.

Code:

Output:

Explanation:

• We defined our lists and passed them to our extend method in python
• extend basically, extended the list2 to the end of list1. The size of the list increased by the length of both lists.
• Also, extend updated our ls1 directly.

5. Using iterable unpacking operator *

An asterisk * denotes iterable unpacking. The unpacking operator takes any iterable(like list, tuple, set, etc.) as a parameter. Then the iterable is expanded into a sequence of items included in the new tuple, list, or set at the site of the unpacking.

Any no. of lists can be concatenated and returned in a new list using this operator. Hence it can be used to merge two lists in Python.

Code:

Output:

Explanation:

• The * first unpacks the contents of ls1, ls2, and ls3 and then creates a list from its contents.
• Then, all the items of our iterables will be added to our new list ls.

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