Python 3: Combine Lists

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Let's say we have two lists, list1 and list2. To combine (merge) these lists into a single list, we can use the + operator:

list1 = [ 'apple', 'orange' ]
list2 = [ 'pineapple', 'blueberry' ]

combined = list1 + list2

print( combined )

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list1 = [ 'apple', 'orange' ]
list2 = [ 'pineapple', 'blueberry' ]

combined = list1 + list2

print( combined )

This code will output:

['apple', 'orange', 'pineapple', 'blueberry']

This works with any number of lists as well:

list1 = [ 'apple', 'orange' ]
list2 = [ 'pineapple', 'blueberry' ]
list3 = [ 'grapefruit', 'mango' ]
list4 = [ 'banana', 'strawberry' ]

combined = list1 + list2 + list3 + list4

print( combined )

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list1 = [ 'apple', 'orange' ]
list2 = [ 'pineapple', 'blueberry' ]
list3 = [ 'grapefruit', 'mango' ]
list4 = [ 'banana', 'strawberry' ]

combined = list1 + list2 + list3 + list4

print( combined )

This code will output:

['apple', 'orange', 'pineapple', 'blueberry', 'grapefruit', 'mango', 'banana', 'strawberry']

To append (concatenate) the items in list2 to the end of list1, we can use the += operator:

list1 = [ 'apple', 'orange' ]
list2 = [ 'pineapple', 'blueberry' ]

list1 += list2

print( list1 )

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list1 = [ 'apple', 'orange' ]
list2 = [ 'pineapple', 'blueberry' ]

list1 += list2

print( list1 )

This code will output list1, which now includes the items from list2:

['apple', 'orange', 'pineapple', 'blueberry']

We can combine the += and + operators to combine more than two lists:

list1 = [ 'apple', 'orange' ]
list2 = [ 'pineapple', 'blueberry' ]
list3 = [ 'grapefruit', 'mango' ]
list4 = [ 'banana', 'strawberry' ]

list1 += list2 + list3 + list4

print( list1 )

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list1 = [ 'apple', 'orange' ]
list2 = [ 'pineapple', 'blueberry' ]
list3 = [ 'grapefruit', 'mango' ]
list4 = [ 'banana', 'strawberry' ]

list1 += list2 + list3 + list4

print( list1 )

This code will output:

['apple', 'orange', 'pineapple', 'blueberry', 'grapefruit', 'mango', 'banana', 'strawberry']

Alternatively, we can use the .extend() method built into Python lists to append all items in list2 to list1:

list1 = [ 'apple', 'orange' ]
list2 = [ 'pineapple', 'blueberry' ]

list1.extend( list2 )

print( list1 )

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list1 = [ 'apple', 'orange' ]
list2 = [ 'pineapple', 'blueberry' ]

list1.extend( list2 )

print( list1 )

Just as with the += operator, this code will output list1, which now includes the items from list2:

['apple', 'orange', 'pineapple', 'blueberry']

Because .extend() is only able to take one list as an argument at a time, to extend by more than one list, we need to call .extend() multiple times:

list1 = [ 'apple', 'orange' ]
list2 = [ 'pineapple', 'blueberry' ]
list3 = [ 'grapefruit', 'mango' ]
list4 = [ 'banana', 'strawberry' ]

list1.extend( list2 )
list1.extend( list3 )
list1.extend( list4 )

print( list1 )

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list1 = [ 'apple', 'orange' ]
list2 = [ 'pineapple', 'blueberry' ]
list3 = [ 'grapefruit', 'mango' ]
list4 = [ 'banana', 'strawberry' ]

list1.extend( list2 )
list1.extend( list3 )
list1.extend( list4 )

print( list1 )

This code will output:

['apple', 'orange', 'pineapple', 'blueberry', 'grapefruit', 'mango', 'banana', 'strawberry']

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