How to Implement a Random String Generator With Python

How to Implement a Random String Generator With Python

Learn how to use Python to create random strings in two different ways, including secure random strings

Play this article

In this post, you'll learn how to create a random string in Python using different methods; but, beware! Some of them only work with Python 3.6+.

By the end of this article, you should be able to:

  • use the choice function to generate a random string from string.ascii_letters, string.digits + string.punctuation characters in Python 3
  • generate a secure random string, useful to create random passwords

Generating a Random String With Upper Case, Lower Case, Digits and Punctuation

The string module comes with a nice set of constants that we can combine with the random module to create our random string.

Using Python's string.ascii_letters + string.digits + string.punctuation Characters

By concatenating string.ascii_letters + string.digits + string.punctuation, we will have our pool of characters that we can pick at random using the random.choices() method. This method returns a k sized list of elements chosen from the population with replacement. In our case, k will be the size of our random string.

>>> import string

>>> string.ascii_letters

>>> string.digits

>>> string.punctuation

>>> all_chars = string.ascii_letters + string.digits + string.punctuation

>>> import random

>>> ''.join(random.choices(all_chars, k=10))

This works well, but there is one limitation: random.choices is available only on Python 3.6+. To make that work in older versions, you'll need to call the random.choice function and iterate over k times.

>>> ''.join((random.choice(all_chars) for _ in range(10)))

How to Generate a Cryptographically Secure Random String

The previous method works well if all we want is a random string for simple use cases. If what we want is a random string to be used as a password, then we need a more secure method. The reason is that the random module does not use a secure pseudo-number generator.

As an alternative we must resort to the Operating System’s pseudo-random number generator. The good news is that Python can access that using the random.SystemRandom class, which ensures that sequences are not reproducible.

We can re-use the previous example and change just one minor detail.

From: random.choices to random.SystemRandom()

>>> all_chars = string.ascii_letters + string.digits + string.punctuation

>>> import random

>>> ''.join(random.SystemRandom().choices(all_chars, k=10))


In this post we saw 2 different ways of creating random strings Python. I hope you find it useful.

Other posts you may like:

See you next time!

This post was originally published at