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Concatenate two lists in Python

Concatenate two lists in Python

David Y.

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The Problem

How can I concatenate two lists in Python? In other words, how can I join two or more lists together to make one big list?

The Solution

We can do this using Python’s built-in operator overloading. When used with lists, the + operator will concatenate them, as shown below:

Click to Copy
list1 = ["Apples", "Oranges", "Bananas"]
list2 = ["Pears", "Grapes", "Pineapples"]

combined = list1 + list2
print(combined)

# output: ['Apples', 'Oranges', 'Bananas', 'Pears', 'Grapes', 'Pineapples']

Alternatively, we can use list.extend(), which will modify the first list:

Click to Copy
list1 = ["Apples", "Oranges", "Bananas"]
list2 = ["Pears", "Grapes", "Pineapples"]

list1.extend(list2)
print(list1)

# output: ['Apples', 'Oranges', 'Bananas', 'Pears', 'Grapes', 'Pineapples']

To concatenate three or more lists, we can also use the + operator:

Click to Copy
list1 = ["Apples", "Oranges", "Bananas"]
list2 = ["Pears", "Grapes", "Pineapples"]
list3 = ["Tangerines", "Apricots"]
list4 = ["Pomegranates", "Watermelons", "Raspberries"]

combined = list1 + list2 + list3 + list4
print(combined)

# output: ['Apples', 'Oranges', 'Bananas', 'Pears', 'Grapes', 'Pineapples', 'Tangerines', 'Apricots', 'Pomegranates', 'Watermelons', 'Raspberries']

However, when combining more than two lists, itertools.chain() is more performant. Note that this method outputs an itertools.chain object, which must be typecast to a list, as shown below:

Click to Copy
from itertools import chain

list1 = ["Apples", "Oranges", "Bananas"]
list2 = ["Pears", "Grapes", "Pineapples"]
list3 = ["Tangerines", "Apricots"]
list4 = ["Pomegranates", "Watermelons", "Raspberries"]

combined = list(chain(list1, list2, list3, list4))
print(combined)

# output: ['Apples', 'Oranges', 'Bananas', 'Pears', 'Grapes', 'Pineapples', 'Tangerines', 'Apricots', 'Pomegranates', 'Watermelons', 'Raspberries']
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