How To Change Indexing In Python

In this tutorial, we will walk through the process of changing indexes in Python, discussing various methods for achieving this goal. This knowledge will enable you to better understand and manipulate data structures in your Python programs.

1. Basic list indexing in Python

In Python, list indexing starts at 0. This means that the first item in the list has an index of 0, the second item an index of 1, and so on.

However, Python also supports negative indexing, which allows us to access elements from the end of the list, with -1 being the last element, -2 being the second to last element, and so on. Let’s start by creating a simple list.

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my_list = [10, 20, 30, 40, 50]

To access the item at index 2, we can use the following code:

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item = my_list[2]
print(item)
 
30

2. Changing list index using slicing

Lists in Python support a technique called slicing, which allows us to create sublists from the original list using a specified range of indices. Slicing uses the following syntax:

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sublist = my_list[start:end]

The “start” value represents the index at which the slice will begin and “end” represents the index at which the slice will end (excluding this index). Let’s say we want to create a sublist that starts from the second element and ends at the fourth element:

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sublist = my_list[1:4]
print(sublist)
 
[20, 30, 40]

We can also step through the list to select items at regular intervals, like this:

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sublist = my_list[0:5:2]
print(sublist)
 
[10, 30, 50]

3. Swapping elements in a list

To change the index of elements in a list, we can simply swap their positions. Let’s say we want to swap the second and fourth elements:

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my_list[1], my_list[3] = my_list[3], my_list[1]
print(my_list)
 
[10, 40, 30, 20, 50]

4. Reversing a list

To reverse the order of elements in a list, we can use a built-in method called reverse():

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my_list.reverse()
print(my_list)
 
[50, 20, 30, 40, 10]

Alternatively, we can use slicing with a step of -1 to create a reversed copy of the list:

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reversed_list = my_list[::-1]
print(reversed_list)
 
[10, 40, 30, 20, 50]

Full code example

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my_list = [10, 20, 30, 40, 50]
 
# access item at index 2
item = my_list[2]
print(item)  # Output: 30
 
# create sublist from second to fourth element
sublist = my_list[1:4]
print(sublist)  # Output: [20, 30, 40]
 
# create sublist with every second element
sublist = my_list[0:5:2]
print(sublist)  # Output: [10, 30, 50]
 
# swap second and fourth elements
my_list[1], my_list[3] = my_list[3], my_list[1]
print(my_list)  # Output: [10, 40, 30, 20, 50]
 
# reverse the list
my_list.reverse()
print(my_list)  # Output: [50, 20, 30, 40, 10]
 
# create reversed copy of the list
reversed_list = my_list[::-1]
print(reversed_list)  # Output: [10, 40, 30, 20, 50]

Output

[20, 30, 40]
[10, 30, 50]
[10, 40, 30, 20, 50]
[50, 20, 30, 40, 10]
[10, 40, 30, 20, 50]

Conclusion

In this tutorial, you’ve learned how to change indexes in Python using various techniques, including basic list indexing, slicing, swapping elements, and reversing the order of elements.

With this knowledge, you’ll be better equipped to manipulate and process data structures in your Python programs.