List and String Slicing

Python provides a helpful utility called slicing that enables us to easily subset a list. Slicing can also be applied to other iterables, such as tuples or strings.

Basic Slicing

Let’s create a list of 5 people.

people = ['amy', 'barry', 'cory', 'diane', 'elaine']

We can select the first and second person in the list without using a for loop by slicing it.

Note 1: Python is zero-indexed, therefore we are looking at the 0th and 1st element in the list.
Note 2: Slicing includes the start index, up to but not including the end index.

print(people[0:2])

['amy', 'barry']

It is also possible to subset the whole list (seems strange for now, but I promise there’s a valid use case for this).

print(people[::])

['amy', 'barry', 'cory', 'diane', 'elaine']

A very useful function of slicing is that it allows us to reverse the order of a list.

print(people[::-1])

['elaine', 'diane', 'cory', 'barry', 'amy']

Slicing by Increments

The third parameter allows us to define the “step”, which allows us to set how the list’s index will increment. This is by default set to 1 (no values are skipped). The code below slices the entire list, and keeps items that are 2 indexes away from each other.

numbers = [1, 2, 3, 4, 5]
print(numbers[::2])

[1, 3, 5]

String Slicing

Slicing can also be applied to strings - simply think of a string as a list of characters.

string = 'The quick brown fox jumps over the lazy dog.'
print(string[0:3])

The

Python allows us to easily reverse a string using the following syntax.

print(string[::-1])

.god yzal eht revo spmuj xof nworb kciuq ehT

This is admittedly not the most useful function that we can apply to a string, but nonetheless we do have the ability to create a new string that skips by a specified number of characters.

print(string[::2])

Teqikbonfxjmsoe h aydg