Python List Index

Lists are one of the most commonly used data structures in Python. They are used to store multiple items in a single variable. In Python, a list can be created by enclosing a sequence of values, separated by commas, inside square brackets [].

To access an item in a list, we use its index. Indexing in Python starts at 0, which means the first item in a list has an index of 0, the second item has an index of 1, and so on.

Accessing items in a list using index

To access an item in a list, we use the square bracket notation followed by the index of the item we want to access. For example,

my_list = ['apple', 'banana', 'cherry', 'orange']
print(my_list[1])   # Output: banana

In the above example, we created a list with four items and printed the second item (index 1) using its index.

Negative indexing

In addition to positive indices, we can also use negative indices to access items in a list. Negative indices count from the end of a list, with -1 being the index of the last item in the list.

my_list = ['apple', 'banana', 'cherry', 'orange']
print(my_list[-1])   # Output: orange

In the above example, we printed the last item in the list (index -1) using negative indexing.

Slicing lists

We can also access a range of items in a list using slicing. Slicing is done using the colon operator ":".

my_list = ['apple', 'banana', 'cherry', 'orange']
print(my_list[1:3])    # Output: ['banana', 'cherry']

In the above example, we printed a range of items from the second item (index 1) to the third item (index 3-1=2) of the list using slicing.

Changing items in a list using index

We can change the value of an item in a list using its index.

my_list = ['apple', 'banana', 'cherry', 'orange']
my_list[1] = 'kiwi'
print(my_list)    # Output: ['apple', 'kiwi', 'cherry', 'orange']

In the above example, we changed the second item (index 1) of the list to 'kiwi' using its index.

Adding and removing items using index

We can add or remove items in a list using its index.

my_list = ['apple', 'banana', 'cherry', 'orange']
my_list.insert(1, 'kiwi')
print(my_list)   # Output: ['apple', 'kiwi', 'banana', 'cherry', 'orange']

my_list.pop(2)
print(my_list)   # Output: ['apple', 'kiwi', 'cherry', 'orange']

In the above example, we added an item ('kiwi') at a specific index (1) using the insert() method and removed an item at a specific index (2) using the pop() method.

Conclusion

In summary, Python list indexing is a powerful tool that allows us to access individual items, ranges of items, and modify items in a list. Understanding list indexing is essential for working with lists in Python.