Python random randrange() and randint() to generate random integer number within a range

In this lesson, we will see how to use the randrange() and randint() functions of a Python random module to generate a random integer number.

Using randrange() and randint() functions of a random module, we can generate a random integer within a range. In this lesson, you’ll learn the following functions to generate random numbers in Python. We will see each one of them with examples.

How to use random.randint()

Syntax:

random.randint(start, stop)Code language: Python (python)

This function returns a random integer between a given start and stop integer.

Parameters:

It takes two parameters. Both are mandatory.

• start: It is the start position of a range. The default value is 0 if not specified.
• stop: It is the end position of a range.

Return value:

It will generate any random integer number from the inclusive range. The randint(start, stop) consider both the start and stop numbers while generating random integers

random.randint() example of generating random number

import random

# random integer from 0 to 9
num1 = random.randint(0, 9)
print(num1)
# output 5

# Random integer from 10 to 100
num2 = random.randint(10, 100)
print(num2)
# Output 84Code language: Python (python)

Note: You cannot use float numbers in randint(). It will raise a ValueError ( non-integer stop for randrange()) if you use non-integer numbers. Please, read how to generate a random float number within a range.

random.randrange() to generate random integers within a range

Now let’s see how to use the random.randrange() function to get a random integer number from the given exclusive range by specifying the increment.

Syntax

random.randrange(start, stop[, step])Code language: Python (python)

This function returns a random integer from a range(start, stop, step). For example, random.randrange(0, 10, 2) will generate any random numbers from [0, 2, 4, 6, 8].

Parameters

It takes three parameters. Out of three, two parameters are optional. i.e., start and step are optional.

• start: it is the star number in a range. i.e., lower limit. The default value is 0 if not specified.
• stop: It is the end/last number in a range. It is the upper limit.
• step: Specify the increment value in range. The generated random number is divisible by step. The default value is 1 if not specified.

random.randrange() examples

In the following example, we are trying to print a random int in a given range. This example demonstrates all the variants of random.randrange() function.

import random

# random integer from 0 to 9
num1 = random.randint(0, 9)
print(num1)
# output 5

# Random integer from 10 to 100
num2 = random.randint(10, 100)
print(num2)
# Output 84Code language: Python (python)

Note:

• The randrange() doesn’t consider the stop number while generating a random integer. It is an exclusive random range. For example, randrange(2, 20, 2) will return any random number between 2 to 20, such as 2, 4, 6, …18. It will never select 20.
• Same as randint(), you cannot use float value in randrange() too. It will raise a ValueError (non-integer arg 1 for randrange()) if you use non-integers.

Random number of a specific length

Let’s see how to generate a random number of length n. For example, any random number of length four, such as 7523, 3674. We can accomplish this using both randint() randrange().

import random

# random number of length 4
num1 = random.randint(1000, 9999)
# random number of length 4 with step 2

num2 = random.randrange(1000, 10000, 2)
print(num1, num2)

# Output 3457 5116
Code language: Python (python)

Note: As you can see, we set a start = 1000 and a stop = 10000 because we want to generate the random number of length 4 (from 1000 to 9999).

Random integer number multiple of n

For example, let’s generate a random number between x and y multiple of 3 like 3, 6, 39, 66.

import random

num = random.randrange(3, 300, 3)
print(num)
# output 144Code language: Python (python)

Random negative integer

Let’s see how to generate a random negative integer between -60 to -6.

import random

singed_int = random.randrange(-60, -6)
print(singed_int)
# Output -16Code language: Python (python)

Generate random positive or negative integer

import random

for i in range(5):
    print(random.randint(-10, 10), end=' ')
# Output 10 -1 5 -10 -7Code language: Python (python)

Randomly generate 1 or -1

import random

num = random.choice([-1, 1])
print(num)Code language: Python (python)

Note: we used random.choice() to choose a single number from the list of numbers. Here our list is [-1, 1].

Generate a list of random integer numbers

In this section, we will see how to generate multiple random numbers. Sometimes we need a sample list to perform testing. In this case, instead of creating it manually, we can create a list with random integers using a randint() or randrange(). In this example, we will see how to create a list of 10 random integers.

import random

random_list = []
# Set a length of the list to 10
for i in range(0, 10):
    # any random numbers from 0 to 1000
    random_list.append(random.randint(0, 1000))
print(random_list)
# Output [994, 287, 65, 994, 936, 462, 839, 160, 689, 624]Code language: Python (python)

Create a list of random numbers without duplicates

Note: In the above example, there is a chance of occurring a duplicate number in a list.

If you want to make sure each number in the list is unique, use the random.sample() method to generate a list of unique random numbers.

• The sample() returns a sampled list of selected random numbers within a range of values.
• It never repeats the element so that we can get a list of random numbers without duplicates

import random

# Generate 10 unique random numbers within a range
num_list = random.sample(range(0, 1000), 10)
print(num_list)
# Output [499, 580, 735, 784, 574, 511, 704, 637, 472, 211]Code language: Python (python)

Note: You can also use the step parameter of the range() function to specify the increment. For example, you want a list of 10 random numbers, but each integer in a list must be divisible by 5, then use random.sample(range(0, 1000, 5), 10)

Sort random numbers list

Use the sort() function to sort a list of random integers in ascending order

import random

sample_list = random.sample(range(50, 500, 5), 5)
# Before sorting
print(sample_list)
# Output [305, 240, 260, 235, 445]

sample_list.sort()
# After sorting
print(sample_list)
# Output [235, 240, 260, 305, 445]
Code language: Python (python)

Generate a secure random integer

Above all, examples are not cryptographically secure. The cryptographically secure random generator generates random numbers using synchronization methods to ensure that no two processes can obtain the same number simultaneously.

If you are producing random numbers for a security-sensitive application, then you must use this approach.

Use the secrets module if you are using a Python version higher than 3.6.

import secrets

# secure random integer
# from 0 to 10
secure_num = secrets.randbelow(10)
print(secure_num)
# Output 5Code language: Python (python)

If you are using Python version less than 3.6, then use the random.SystemRandom().randint() or random.SystemRandom().randrange() functions.

Create a multidimensional array of random integers

Python’s NumPy module has a numpy.random package to generate random data. To create a random multidimensional array of integers within a given range, we can use the following NumPy methods:

• randint()
• random_integers()
• np.randint(low[, high, size, dtype]) to get random integers array from low (inclusive) to high (exclusive).
• np.random_integers(low[, high, size]) to get random integer’s array between low and high, inclusive.

Now, Let see the example.

Generate a 4 x 4 array of ints between 10 and 50, exclusive:

import numpy

# 4 x 4 array
newArray = numpy.random.randint(10, 50, size=(4, 4))
print(newArray)Code language: Python (python)

Output:

[[10 48 30 24]
 [13 46 30 11]
 [12 28 49 26]
 [30 18 49 35]]

Generate a 5 x 3 array of random integers between 60 and 100, inclusive.

import numpy

# 3 x 5 array of ints
newArray = numpy.random.random_integers(60, 100, size=(3, 5))
print(newArray)Code language: Python (python)

Output:

[[63 76 95 93 75]
 [71 84 63 99 93]
 [65 64 66 69 92]]

Points to remember about randint() and randrange()

• Use randint() when you want to generate a random number from an inclusive range.
• Use randrange() when you want to generate a random number within a range by specifying the increment. It produces a random number from an exclusive range.

You should be aware of some value constraints of a randrange() function.

• The randint() rand randrange() works only with integers. You cannot use float numbers.
• The step must not be 0. If it is set to 0, you will get a ValueError: zero step for randrange()
• The start should not be greater than stop if you are using all positive numbers. If you set start greater than stop, you will get a ValueError: empty range for randrange()

Examples

import random

# ValueError: empty range for randrange()
print(random.randrange(100, 10, 2))Code language: Python (python)

But, you can also set a start value greater than stop if you are using a negative step value.

import random

print(random.randrange(100, 10, -2))
# output 60Code language: Python (python)

Next Steps

I want to hear from you. What do you think of this article on randint() and randrange()? Or maybe I missed one of the usages of those two functions. Either way, let me know by leaving a comment below.

Also, try to solve the following exercise and quiz to have a better understanding of working with random data in Python.

• Python random data generation Exercise to practice and master the random data generation techniques in Python.
• Python random data generation Quiz to test your random data generation concepts.