6 Ways to Concatenate Lists in Python

In Python, there are several ways to concatenate lists. Here are six methods you can use:

1. Using the + Operator:

   The + operator allows you to concatenate two lists together.

                   
                       list1 = [1, 2, 3]
                       list2 = [4, 5, 6]
                       result = list1 + list2
                       print(result)  # Output: [1, 2, 3, 4, 5, 6]                    
                   
               

2. Using the extend() Method:

   The extend() method appends the elements of one list to the end of another list.

                   
                       list1 = [1, 2, 3]
                       list2 = [4, 5, 6]
                       list1.extend(list2)
                       print(list1)  # Output: [1, 2, 3, 4, 5, 6]                    
                   
               

3. Using List Comprehension:

   You can use list comprehension to combine multiple lists.

                   
                       list1 = [1, 2, 3]
                       list2 = [4, 5, 6]
                       list3 = [7, 8, 9]
                       result = [item for lst in [list1, list2, list3] for item in lst]
                       print(result)  # Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]                    
                   
               

4. Using the itertools.chain() Function:

   The itertools.chain() function allows you to concatenate multiple lists efficiently.

                   
                       from itertools import chain
   
                       list1 = [1, 2, 3]
                       list2 = [4, 5, 6]
                       list3 = [7, 8, 9]
                       result = list(chain(list1, list2, list3))
                       print(result)  # Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]                    
                   
               

5. Using the * Operator (unpacking):

   The unpacking operator * can be used in a function call to concatenate lists.

                   
                       list1 = [1, 2, 3]
                       list2 = [4, 5, 6]
                       list3 = [7, 8, 9]
                       result = [*list1, *list2, *list3]
                       print(result)  # Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]                    
                   
               

6. Using the list constructor with sum() function:

   You can use the sum() function with the list constructor to concatenate lists. However, note that sum() with a list of lists may not be as efficient as other methods, as it is more suited for numbers.

                   
                       list1 = [1, 2, 3]
                       list2 = [4, 5, 6]
                       list3 = [7, 8, 9]
                       result = list(sum([list1, list2, list3], []))
                       print(result)  # Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]                    
                   
               

These are some ways to concatenate lists in Python. Choose the method that best suits your needs based on readability, performance, and coding style preferences.

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