Python range() Function — A Helpful Illustrated Guide

The Python range() function creates an iterable of subsequent integers within a given range of values. You can pass either only a stop argument in which case the range object will include all integers from 0 to stop (excluded). Or you can pass start, stop, and step arguments in which case the range object will go from start to step using the given step size. For example, range(3) results in 0, 1, 2 and range(2, 7, 2) results in 2, 4, 6.

Here are some examples of how to use the range() built-in function:

>>> range(10)
range(0, 10)
>>> print(range(10))
range(0, 10)
>>> print(*range(10))
0 1 2 3 4 5 6 7 8 9
>>> range(1, 10, 3)
range(1, 10, 3)
>>> print(*range(1, 10, 3))
1 4 7

Note that in any case, a range object is returned. The range object is an iterable of values—but the values are only generated as they’re actually needed. You can use the asterisk operator to unpack all values into the print function with print(*range(10)). Python waits as long as possible to generate the values of the iterable.

Syntax Range Function

You can use the range() function with three different argument lists: (i) with the stop argument only, (ii) with the start and stop arguments, or (iii) with the start, stop, and step arguments.

Syntax: 
range(stop)
range(start, stop)
range(start, stop, step)

Interesting fact: the range() “function” is technically not a normal function but a constructor method of the range class. Thus, it creates a new range object.

How Math Genius Gauss Hacked His Teacher’s Exercise With the Range Function

Do you know the following story of the brilliant mathematician Carl Friedrich Gauss? When 8-year old Gauss went to school, his math teacher sought a few minutes of breathing pause. He told his class to solve the problem of adding all subsequent numbers from 1-100: 1+2+3+...+100.

But as little Gauss promptly reported the solution, the short pause was over before it began.

Surprised (and a bit grumpy as the story goes), the teacher asked the boy how he had come up with a solution so quickly. Gauss explained his simple solution. He organized the sequence into pairs of numbers each summing up to 101: 1+100,2+99,3+98,...,50+51. There are 50 such pairs, so the total result was 50*101=5050.

Yet, the modern-time little Gauss would be even lazier. He would type the following one-liner into his mobile Python app: sum(range(1,101)).

The range() function returns a sequence starting from the first value (inclusive) and ending in the second value (exclusive). The sum function sums up the values of this sequence. Combining both functions sums up the sequence from 1-100—faster than the brilliant Carl Friedrich Gauss.

Python range() With One Argument Stop

You can use the range() function with one argument stop. In this case, the range object goes from start=0 to the stop argument (excluded) by using the default step size of one.

Here’s the example:

for i in range(5):
    print(i)

The output is:

0
1
2
3
4

Python range() With Two Arguments Start + Stop

You can use the range() function with two arguments start and stop. In this case, the range object goes from start to the stop integer value (excluded) by using the default step size of one.

Here’s the example:

for i in range(1, 5):
    print(i)

The output is:

1
2
3
4

Python range() With Three Arguments Start + Stop + Step

You can use the range() function with three arguments start, stop, and step. In this case, the range object goes from start to the stop integer value (excluded) by using the default step size of step.

Here’s the example:

for i in range(1, 5, 2):
    print(i)

The output is:

1
3

Interactive Shell Exercise About The Range Function

The following code snippet matches men with women—the idea is to match the i-th man with the i-th woman, assuming that both lists have the same size. How to change the code to accomplish this task?

Exercise: Replace the XXXX placeholder in the code to match the i-th man with the i-th woman!

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Solution: The following code solves the exercise.

men = ['Bob', 'Carl', 'Frank']
women = ['Ann', 'Alice', 'Liz']

for i in range(len(men)):
    print(men[i] + ' dances with ' + women[i])

The idea is to use the len() function to determine the stop argument automatically with range(len(men)). Note that range(len(women)), range(3), and range(0, 3), and range(0, 3, 1) would all solve the problem equally well.

Python range() With Negative Step Size

You can also use the range() function with negative step size. The meaning is “move from right to the left using the negative step size as the difference between two subsequent values. In this case, the start argument should be larger than the stop argument.

Here’s an example:

for i in range(4,0,-2):
    print(i)

The output is:

4
2

Note that the stop argument is still not included in the range object.

Range Puzzle

Puzzles are a great and effective way to improve your Python skills. Can you solve this range puzzle?

# Python Puzzle
print(sum(range(0,7)))

What is the output of this code snippet?

You can check whether you solved this puzzle correctly, and determine whether you’re a master coder on our Puzzle app Finxter.com:

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Summary

The Python range() function creates an iterable of subsequent integers within a given range of values.

You can pass either only a stop argument in which case the range object will include all integers from 0 to stop (excluded). For example, range(3) results in 0, 1, 2:

for i in range(3):
    print(i)
    
'''
OUTPUT:
0
1
2
'''

As an alternative, you can pass start, stop, and step arguments in which case the range object will go from start to step using the given step size. For example, range(2, 7, 2) results in 2, 4, 6:

for i in range(2, 7, 2):
    print(i)
    
'''
OUTPUT:
2
4
6
'''

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