How to Generate Random Strings in Python

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Python Random String Generation

In this article, we’ll take a look at how we can generate random strings in Python. As the name suggests, we need to generate a random sequence of characters, it is suitable for the random module.

There are various approaches here, so we’ll start from the most intuitive one; using randomized integers.

Build a string from a random integer sequence

As you may know, the chr(integer) maps the integer to a character, assuming it lies within the ASCII limits. (Taken to be 255 for this article)

We can use this mapping to scale any integer to the ASCII character level, using chr(x), where x is generated randomly.

import random

# The limit for the extended ASCII Character set
MAX_LIMIT = 255

random_string = ''

for _ in range(10):
    random_integer = random.randint(0, MAX_LIMIT)
    # Keep appending random characters using chr(x)
    random_string += (chr(random_integer))

print(random_string, len(random_string))

Sample Output

ð|ÒR:
     Rè 10

Here, while the length of the string seems to be 10 characters, we get some weird characters along with newlines, spaces, etc.

This is because we considered the entire ASCII Character set.

If we want to deal with only English alphabets, we can use their ASCII values.

import random

random_string = ''

for _ in range(10):
    # Considering only upper and lowercase letters
    random_integer = random.randint(97, 97 + 26 - 1)
    flip_bit = random.randint(0, 1)
    # Convert to lowercase if the flip bit is on
    random_integer = random_integer - 32 if flip_bit == 1 else random_integer
    # Keep appending random characters using chr(x)
    random_string += (chr(random_integer))

print(random_string, len(random_string))

Sample Output

wxnhvYDuKm 10

As you can see, now we have only upper and lowercase letters.

But we can avoid all this hassle, and have Python do the work for us. Python has given us the string module for exactly this purpose!

Let’s look at how we can do the same this, using just a couple of lines of code!

Generate Random Strings in Python using the string module

The list of characters used by Python strings is defined here, and we can pick among these groups of characters.

We’ll then use the random.choice() method to randomly choose characters, instead of using integers, as we did previously.

Let us define a function random_string_generator(), that does all this work for us. This will generate a random string, given the length of the string, and the set of allowed characters to sample from.

import random
import string

def random_string_generator(str_size, allowed_chars):
    return ''.join(random.choice(allowed_chars) for x in range(str_size))

chars = string.ascii_letters + string.punctuation
size = 12

print(chars)
print('Random String of length 12 =', random_string_generator(size, chars))

Here, we have specified the allowed list of characters as the string.ascii_letters (upper and lowercase letters), along with string.punctuation (all punctuation marks).

Now, our main function was only 2 lines, and we could randomly choose a character, using random.choice(set).

Sample Output

abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
Random String of length 12 = d[$Om{;#cjue

We have indeed generated a random string, and the string module allows easy manipulations between character sets!

Make the random generation more secure

While the above random generation method works, if you want to make your function be more cryptographically secure, use the random.SystemRandom() function.

An example random generator function is shown below:

import random
import string

output_string = ''.join(random.SystemRandom().choice(string.ascii_letters + string.digits) for _ in range(10))

print(output_string)

Output

iNsuInwmS8

This ensures that your string generation is cryptographically secure.

Random UUID Generation

If you want to generate a random UUID String, the uuid module is helpful for this purpose.

import uuid

# Generate a random UUID
print('Generated a random UUID from uuid1():', uuid.uuid1())
print('Generated a random UUID from uuid4():', uuid.uuid4())

Sample Output

Generated a random UUID from uuid1(): af5d2f80-6470-11ea-b6cd-a73d7e4e7bfe
Generated a random UUID from uuid4(): 5d365f9b-14c1-49e7-ad64-328b61c0d8a7

Conclusion

In this article, we learned how we could generate random strings in Python, with the help of the random and string modules.

References