Python Random randrange() Method

Usage

The randrange() method returns an integer number randomly selected from the specified range.

Syntax

random.randrange(start, stop, step)

Parameters

Module Import

To use the randrange() method, you need to import the random module first.

import random

How to use the randrange() Function?

There are three ways to use the randrange() function:

• randrange(stop): With only the stop argument provided, you will get a random integer between 0 (inclusive) and the number you specify as the stop (exclusive).
• randrange(start, stop): When you provide both start and stop arguments, you define both the lower bound (start) and upper bound (stop) of the desired range of random numbers.
• randrange(start, stop, step): By including the step argument, you determine the increment between possible random numbers within the range.

Let’s break down each use case with examples.

randrange(stop)

When you call randrange() with just one argument, you will get a random integer between 0 (inclusive) and the number you specify as the stop (exclusive).

import random

# Generate a random number between 0 and 10 (exclusive)
print(random.randrange(10))
# Possible output: 6

In this example, only the stop parameter is set to 10. This means the method will generate a random integer starting from the default start value, which is 0, up to but not including 10. So the possible values that can be generated are: 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9.

Below are some more examples:

print(random.randrange(100))
# Possible output: 53

print(random.randrange(50))
# Possible output: 49

randrange(start, stop)

When you call randrange() with two arguments, you get to decide not only the upper bound but also the lower bound of the range, so your range does not always start at 0.

Let’s see how to generate a random integer between 5 and 10 (exclusive):

print(random.randrange(5, 10))
# Possible output: 6

In this example, both the start and stop parameters are provided. The method will produce a random integer between the value of start (which is 5 in this case) up to but not including the stop value (which is 10). So the possible values that can be generated are: 5, 6, 7, 8, or 9.

Below are some more examples:

print(random.randrange(60, 100))
# Possible output: 73

print(random.randrange(150, 1000))
# Possible output: 428

You can generate a negative random number as well.

print(random.randrange(-10, 10))
# Possible output: -2

randrange(start, stop, step)

When you call randrange() with three arguments, you not only specify the lower and upper bounds of the range but also the interval between potential numbers. If you do not specify a step value, randrange() will assume that the step is 1.

print(random.randrange(5, 20, 5))
# Possible output: 15

In this example, all three parameters start, stop, and step are provided. The method will generate a random integer from the range starting from 5 (inclusive) to 20 (exclusive), but only in increments defined by the step value of 5. So, the method considers values 5, 10, and 15 as potential outputs.

Below are some more examples:

print(random.randrange(3, 30, 3))
# Possible output: 24

print(random.randrange(7, 70, 7))
# Possible output: 7

When the step is negative, the range of possible values is generated in descending order, starting from the start value and moving towards the stop value, but not including the stop value itself.

print(random.randrange(50, 10, -5))
# Possible output: 15

print(random.randrange(50, -50, -10))
# Possible output: -40

If the range defined by the start, stop, and step arguments is empty, randrange() will raise a ValueError.

print(random.randrange(-10))
# Triggers ValueError: empty range for randrange()

print(random.randrange(50, 10))
# Triggers ValueError: empty range for randrange()

print(random.randrange(10, 50, -5))
# Triggers ValueError: empty range for randrange()

randrange() vs randint()

While both randrange() and randint() are useful for generating random integers, they have subtle differences in how they work.

• randint(start, stop) returns a random integer within a completely inclusive range. This means both the start and stop values you provide can be included in the possible results.
• On the other hand, randrange([start], stop[, step]) offers more flexibility. It generates a random integer within a range where the stop value is exclusive (meaning it won’t be included as a possible result). Additionally, the optional step argument allows you to specify the increments between potential outcomes.

In a nutshell, randint(start, stop) is equivalent to calling randrange(start, stop + 1).

So, randint() is straightforward and more suitable when you need a random integer within a specified range, including both endpoints. However, if you require more fine-grained control over the range, especially with regular intervals other than 1, randrange() is the preferable choice.