The random Module

For the last few lessons, we have been using the turtle module. Another module that we will use often in this class is the random module, a simple Python library that lets us create (pseudo)random numbers.

random.randrange()

randrange() is a command that functions much like range() with start and stop parameters, but produces random integers instead. Here’s an example:

import random

for i in range(5):
    print(random.randrange(1, 11))  # prints a random integer from 1 to 10

We can also use the step parameter with random.randrange():

import random

for i in range(5):
    print(random.randrange(1, 11, 2))  # prints a random ODD integer from 1 to 10

random.randint()

randint() works exactly like random.randrange(), but the stop value is included as a possible value. So print(random.randrange(1,20)) would print a random integer from 1 to 20.

random.random()

The last command from the random module is random.random(), which returns a random float value between 0 and 1. At first, this may seem fairly useless, until you remember that a random decimal between 0 and 1 is equivalent to a random percentage. One very helpful application of to use random.random() to create random colors.

The turtle module allows us to set pen colors and fill colors by either entering a color string (like “blue” or “lightgreen”) or by entering an RGB value (red-green-blue). An RGB value is a set of three percentages that correspond to the percentage of red, the percentage of green, and the percentage of blue to use in the selected color. Since random.random() returns a random percentage in decimal form, we can use it to create a random color:

import random

import turtle

wn = turtle.Screen()
wn.bgcolor(random.random(), random.random(), random.random())   # selects a random background color

bob = turtle.Turtle()

wn.exitonclick()

Exercises:

  1. Use a for loop to print 10 random numbers.
  2. Use a for loop to print ten random even numbers between 1 and 1000. 1000 should be a possible answer.