In this article, you will learn how to use the range() function in Python with the help of code examples along the way.
What is the range() Function in Python? range() Function Syntax Breakdown
Python's built-in range() function is mainly used when working with for loops – you can use it to loop through certain blocks of code a specified number of times.
The range() function accepts three arguments – one is required, and two are optional.
By default, the syntax for the range() function looks similar to the following:
range(stop)
The stop argument is required.
The range() function returns a sequence of numbers starting from 0, incrementing by 1, and ending at the value you specify as stop (non-inclusive).
But what if you want to iterate through a range of two numbers you specify and don't want to start the counting from 0?
You can pass a second optional start argument, start, to specify the starting number. The syntax to do so looks like this:
range(start, stop)
This syntax generates a sequence of numbers based on the start (inclusive) and stop (non-inclusive) values that increment by 1.
Lastly, if you don't want the default increment to be 1, you can specify a third optional argument, step. The syntax to do that looks like this:
range(start, stop, step)
This syntax generates a sequence of numbers that starts counting at start (inclusive) and increments according to step until it reaches stop (non-inclusive).
How to Use the range() Function with Only the stop Argument
When using only the stop argument with range(), the counting starts at 0 and increments by 1. The counting stops when you reach the value you specify as stop.
Keep in mind that the stop value you specify is not inclusive!
If you specify a stop argument of 5, the range includes the numbers 0 - 4 and not 0 - 5 – the counting will stop at 4 and not 5.
Let's take a look at the example below:
for num in range(5):
print(num)
# output
# 0
# 1
# 2
# 3
# 4
In this example, I specified a range(5).
The function started counting from 0, incremented by 1 on each iteration and ended at 4.
How to Use the range() Function with the start And stop Arguments
If you want to have a range of two numbers, you use two arguments – start and stop. Keep in mind that the start value is inclusive, whereas the stop value is not.
If you want a range of values from 5 inclusive to 10 inclusive, you write a range(5,11) like so:
for num in range(5,11):
print(num)
# output
# 5
# 6
# 7
# 8
# 9
# 10
You can pass negative integer values to range() as well:
for num in range(-5, 1):
print(num)
# output
# -5
# -4
# -3
# -2
# -1
# 0
Something to note here is that you cannot pass float values to range().
In this example, when I pass two float values as arguments, an error gets raised:
for num in range(5.2, 4.3):
print(num)
# output
# Traceback (most recent call last):
# File "main.py", line 1, in <module>
# for num in range(5.2, 4.3):
# TypeError: 'float' object cannot be interpreted as an integer
You can pass either negative or positive integers as start and stop arguments.
How to Use the range() Function with the start, stop, And step Arguments
By default, the increment value is 1 and is not specified. That said, you can change it by passing a step argument to the range() function.
Let's take a look at the following example:
for num in range(10,21,2):
print(num)
# output
# 10
# 12
# 14
# 16
# 18
# 20
In the example above, I generated a sequence of numbers from 10 to 20 and incremented the steps by 2. I achieved this by specifying a step value of 2.
Something to note is that step can be either a negative or positive number, but it cannot be 0.
Here is how you can generate a range with a negative step argument:
for num in range(20, 11, -2):
print(num)
# output
# 20
# 18
# 16
# 14
# 12
The code above generates a sequence of numbers in reverse.
And look at what happens when the step is 0:
for num in range(10, 21 0):
print(num)
# output
# File "main.py", line 1
# for num in range(10, 21 0):
^
# SyntaxError: invalid syntax
How to Create A List of Numbers Using the range() Function
You can create a list of numbers by passing the range() function as an argument to the list() constructor like so:
my_numbers_list = list(range(5))
print(my_numbers_list)
# output
# [0, 1, 2, 3, 4]
In the example above, I created a list of numbers from 0 to 4.
How to use The len() Function with range() in Python
Say you have a list of items and want to do something to the items depending on how long the list is.
For that, you could use range() and pass the length of your list as an argument to the function.
To calculate the length of a list, use the len() function.
programming_languages = ["Python", "JavaScript", "Java", "C++"]
programming_languages_length = len(programming_languages)
for languages in range(programming_languages_length):
print("Hello World")
# output
# Hello World
# Hello World
# Hello World
# Hello World
Conclusion
And there you have it! You now know how to use the range() function in Python.
To learn more about Python, check out freeCodeCamp's Python for beginners course.
Thanks for reading, and happy coding!