Python random module
last modified January 29, 2024
Python random module tutorial shows how to generate pseudo-random numbers in Python.
Random number generator
Random number generator (RNG) generates a set of values that do not display any distinguishable patterns in their appearance. The random number generators are divided into two categories: hardware random-number generators and pseudo-random number generators. Hardware random-number generators are believed to produce genuine random numbers. Pseudo-random number generators generate values based on software algorithms. They produce values that look random. But these values are deterministic and can be reproduced, if the algorithm is known.
In computing, random generators are used in gambling, gaming, simulations, or cryptography.
To increase the quality of the pseudo random-number generators, operating systems use environmental noise collected from device drivers, user input latency, or jitter from one or more hardware components. This is the core of the cryptographically secure pseudo-random number generators.
Python random module
The built-in Python random module implements pseudo-random number generators for
various distributions. Python uses the Mersenne Twister algorithm to produce its
pseudo-random numbers. This module is not suited for security. For security related
tasks, the secrets module is recommended.
The seed
The seed is a value which initializes the random number generator. Random number generators produce values by performing some operation on a previous value. When the algorithm starts, the seed is the initial value on which the generator operates. The most important and difficult part of the generators is to provide a seed that is close to a truly random number.
In Python, the seed value is provided with the random.seed function. If the value
is not explicitly given, Python uses either the system clock or other random source.
Python random - same seed
In the following example, we use the same seed.
#!/usr/bin/python
import random
myseed = 16
random.seed(myseed)
print(random.random())
print(random.random())
print(random.random())
print('********************************')
random.seed(myseed)
print(random.random())
print(random.random())
print(random.random())
The same seed value produces the same pseudo-random values.
$ ./same_seed.py 0.36152277491407514 0.480480665601294 0.4169526266056648 ******************************** 0.36152277491407514 0.480480665601294 0.4169526266056648
Python random.randint
The random.randint function generates integers between values [x, y].
#!/usr/bin/python import random val = random.randint(1, 10) print(val) val = random.randint(1, 10) print(val) val = random.randint(1, 10) print(val) val = random.randint(1, 10) print(val)
The example produces four random integers between numbers 1 and 10.
$ ./rand_int.py 10 4 9 3
Python random.randrange
The random.randrange function excludes the right-hand side of the interval.
It picks values between [x, y).
#!/usr/bin/python import random val = random.randrange(1, 10) print(val) val = random.randrange(1, 10) print(val) val = random.randrange(1, 10) print(val) val = random.randrange(1, 10) print(val)
The example produces four random integers between numbers 1 and 10, where the value 10 is excluded.
Python random.uniform
The random.uniform function generates random floats between
values [x, y].
#!/usr/bin/python import random val = random.uniform(1, 10) print(val) val = random.uniform(1, 10) print(val) val = random.uniform(1, 10) print(val) val = random.uniform(1, 10) print(val)
The example produces four random floats between numbers 1 and 10.
$ ./floats.py 9.594596536362012 5.832673168195081 6.7942727933257 7.035310921661894
Python random.choice
The random.choice function returns a random element
from the non-empty sequence.
#!/usr/bin/python import random words = ['sky', 'storm', 'rock', 'falcon', 'forest'] val = random.choice(words) print(val) val = random.choice(words) print(val) val = random.choice(words) print(val) val = random.choice(words) print(val)
The example picks randomly a word from the list four times.
$ ./rand_choice.py forest forest sky storm
Python random.shuffle
The random.shuffle function shuffles the sequence in place.
#!/usr/bin/python import random words = ['sky', 'storm', 'rock', 'falcon', 'forest'] random.shuffle(words) print(words) random.shuffle(words) print(words)
The example shuffles the list of words twice.
$ ./shuffling.py ['storm', 'falcon', 'rock', 'sky', 'forest'] ['falcon', 'storm', 'rock', 'forest', 'sky']
Python random.sample
The random.sample allows to pick a random sample
of n unique elements from a sequence.
#!/usr/bin/python import random words = ['sky', 'storm', 'rock', 'falcon', 'forest'] sample = random.sample(words, 3) print(sample) sample = random.sample(words, 3) print(sample)
The example picks randomly three elements twice from a list of words.
$ ./sampling.py ['rock', 'storm', 'falcon'] ['forest', 'sky', 'rock']
Python secrets
The secrets module is used for generating cryptographically strong random numbers suitable for managing data such as passwords, account authentication, or security tokens.
#!/usr/bin/python import secrets import string print(secrets.token_hex(12)) print(secrets.token_urlsafe(12)) alphabet = string.ascii_letters + string.digits password = ''.join(secrets.choice(alphabet) for i in range(8)) print(password)
The token_hex function returns a random text string, in hexadecimal.
The token_urlsafe function returns a random URL-safe text string.
alphabet = string.ascii_letters + string.digits password = ''.join(secrets.choice(alphabet) for i in range(8))
Here we generate an eight-character alphanumeric password.
$ ./strong.py 69e6919fc04cbd6f9f5a25dc eLL8-yT4cictksh8 YbpPzXvt
Source
random — Generate pseudo-random numbers
In this article we have worked with the Python random module.
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