Random Numbers in Python

Python defines a set of functions that are used to generate or manipulate random numbers through the random module. 

Functions in the random module rely on a pseudo-random number generator function random(), which generates a random float number between 0.0 and 1.0. These particular type of functions is used in a lot of games, lotteries, or any application requiring a random number generation.

Let us see an example of generating a random number in Python using the random() function.

Python3

import random
num = random.random()
print(num)

Output:

0.30078080420602904

Different Ways to Generate a Random Number in Python

There are a number of ways to generate a random numbers in Python using the functions of the Python random module. Let us see a few different ways.

Generating a Random number using choice()

Python random.choice() is an inbuilt function in the Python programming language that returns a random item from a list, tuple, or string.

Python3

# import random
import random

# prints a random value from the list
list1 = [1, 2, 3, 4, 5, 6]
print(random.choice(list1))

# prints a random item from the string
string = "striver"
print(random.choice(string))

Output:

5
t

Generating a Random Number using randrange()

The random module offers a function that can generate Python random numbers from a specified range and also allows room for steps to be included, called randrange().

Python3

# importing "random" for random operations
import random

# using choice() to generate a random number from a
# given list of numbers.
print("A random number from list is : ", end="")
print(random.choice([1, 4, 8, 10, 3]))

# using randrange() to generate in range from 20
# to 50. The last parameter 3 is step size to skip
# three numbers when selecting.
print("A random number from range is : ", end="")
print(random.randrange(20, 50, 3))

Output:

A random number from list is : 4
A random number from range is : 41

Generating a Random number using seed()

Python random.seed() function is used to save the state of a random function so that it can generate some random numbers in Python on multiple executions of the code on the same machine or on different machines (for a specific seed value). The seed value is the previous value number generated by the generator. For the first time when there is no previous value, it uses the current system time.

Python3

# importing "random" for random operations
import random

# using random() to generate a random number
# between 0 and 1
print("A random number between 0 and 1 is : ", end="")
print(random.random())

# using seed() to seed a random number
random.seed(5)

# printing mapped random number
print("The mapped random number with 5 is : ", end="")
print(random.random())

# using seed() to seed different random number
random.seed(7)

# printing mapped random number
print("The mapped random number with 7 is : ", end="")
print(random.random())

# using seed() to seed to 5 again
random.seed(5)

# printing mapped random number
print("The mapped random number with 5 is : ", end="")
print(random.random())

# using seed() to seed to 7 again
random.seed(7)

# printing mapped random number
print("The mapped random number with 7 is : ", end="")
print(random.random())

Output:

A random number between 0 and 1 is : 0.510721762520941
The mapped random number with 5 is : 0.6229016948897019
The mapped random number with 7 is : 0.32383276483316237
The mapped random number with 5 is : 0.6229016948897019
The mapped random number with 7 is : 0.32383276483316237

Generating a Random number using shuffle()

The shuffle() function is used to shuffle a sequence (list). Shuffling means changing the position of the elements of the sequence. Here, the shuffling operation is in place.

Python3

# import the random module
import random


# declare a list
sample_list = ['A', 'B', 'C', 'D', 'E']

print("Original list : ")
print(sample_list)

# first shuffle
random.shuffle(sample_list)
print("\nAfter the first shuffle : ")
print(sample_list)

# second shuffle
random.shuffle(sample_list)
print("\nAfter the second shuffle : ")
print(sample_list)

Output:

Original list : 
['A', 'B', 'C', 'D', 'E']

After the first shuffle : 
['A', 'B', 'E', 'C', 'D']

After the second shuffle : 
['C', 'E', 'B', 'D', 'A']

Generating a Random number using uniform()

The uniform() function is used to generate a floating point Python random number between the numbers mentioned in its arguments. It takes two arguments, lower limit(included in generation) and upper limit(not included in generation).

Python3

# Python code to demonstrate the working of
# shuffle() and uniform()

# importing "random" for random operations
import random

# Initializing list
li = [1, 4, 5, 10, 2]

# Printing list before shuffling
print("The list before shuffling is : ", end="")
for i in range(0, len(li)):
    print(li[i], end=" ")
print("\r")

# using shuffle() to shuffle the list
random.shuffle(li)

# Printing list after shuffling
print("The list after shuffling is : ", end="")
for i in range(0, len(li)):
    print(li[i], end=" ")
print("\r")

# using uniform() to generate random floating number in range
# prints number between 5 and 10
print("The random floating point number between 5 and 10 is : ", end="")
print(random.uniform(5, 10))

Output:

The list before shuffling is : 1 4 5 10 2 
The list after shuffling is : 2 1 4 5 10 
The random floating point number between 5 and 10 is : 5.183697823553464