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Generate random integers within a range in Python

Generate random integers within a range in Python

David Y.

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The Problem

Using Python, how do I get a random integer within a particular range, for example, between 0 and 9?

The Solution

If we’re using randomness for a non-security purpose, such as modeling a system or building a game, we can generate pseudorandom numbers with the built-in Python random module. This module provides two different functions that will serve our purpose, randrange and randint. Consider the following code:

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import random

random_one = random.randrange(0,9) # will produce one of [0,1,2,3,4,5,6,7,8]
random_two = random.randint(0,9) # will produce one of [0,1,2,3,4,5,6,7,8,9]

The randrange function will produce an integer between the first and second arguments, exclusive of the second. The randint function will produce an integer inclusive of the second argument. Behind the scenes, randint is merely an alias for randrange(start, stop+1).

The randrange function can also take a step argument, allowing us to skip elements of the provided range. For example, if we wanted to select any even number between 0 and 9, we could use a step of 2, as below:

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import random

random_even = random.randrange(0,9,2) # will produce one of [0,2,4,6,8]

As noted in a warning near the top of the random module’s documentation, values produced by its generators should not be used for security purposes. For that, we’ll need the secrets module, which provides a randbelow method we can use to generate a random integer between 0 and the provided argument, exclusive.

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import secrets

secure_random = secrets.randbelow(10) # will produce one of [0,1,2,3,4,5,6,7,8,9]

Should we want a random number with a higher starting point than 0, as is possible with randrange, we can add our starting point to the result, as below:

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import secrets

secure_random = 1 + secrets.randbelow(10) # will produce one of [1,2,3,4,5,6,7,8,9,10]
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