Random Integers

4.3. Random Integers#

It is often useful for computer programs to be able to produce random results. For example, games and numerical simulations involve elements of randomness. Randomness can be achieved using a random number generator. In Python, we can create random numbers using the random module. We will need to import the module at the start of our program to use it.

import random

We can generate random integers using random.randrange(), which is very similar to the range() function. The structure of the random.``randrange()`` function is:

random.randrange(end)

random.randrange(start, end)

random.randrange(start, end, step_size)

Note

The start value is included while the end value is excluded and the start, end, and step_size must be integers.

Example random.randrange(end): By default the start value is 0, so this will generate random number between 0 and end, but does not include the end value. Try running the code below multiple times. You will find it will give you 0, 1 or 2.

import random

print(random.randrange(3))

Example random.randrange(start, end): This will generate random integers between the specified start and end values but does not include the end value. The code below will give you either a 5, 6 or 7.

import random

print(random.randrange(5, 8))

Example random.randrange(start, end, step_size): This will generate random integers between the specified start and end values, counting up by the specified step. It will not include the end value. The code below will give you either 10, 12, 14, 16 or 18.

import random

print(random.randrange(10, 20, 2))

Generating integers allows us to randomly select from lists. For example, the code below will allow us to randomly select a starting player.

import random

players = ["Alice", "Bob"]
i = random.randrange(
    len(players)
)  # len(players) is 2, so this will randomly generate either 0 or 1

print(players[i])
Question 1

Which of the following values could you obtain after running the following program? Select all that apply.

import random

print(random.randrange(5))

  1. 0

  2. 1

  3. 2

  4. 3

  5. 4

  6. 5

Solution

A. B. C. D. E.

When only one value is specified random.randrange() will return integers between 0 up to but not including the end value. In this example, the end value is 5, which means the program will return values 0, 1, 2, 3 and 4.

Question 2

Write a program that will randomly assign a players to the red, blue or green team. Each time the program runs it should display either red, green or blue with equal likelihood.

Solution

Solution is locked

Question 3

You live at 25 Welcome Street. You want to set yourself a reminder each week to drop in and say hi to your neighbours on your side of the street. You’re friends with the residents from 21 to 35. Write a program that randomly selects a neighbour to say hi to.

Your program should output

Say hi to X!

where X is a randomly generated house number from 21 to 35 inclusive. Note that your program should never select 25 (since it’s silly to say hi to yourself) and your program should only select odd numbered houses as your side of the street is odd.

Why won’t the following program work?

import random

r = random.randrange(21, 37, 2)

if r == 25:
    r = random.randrange(21, 37, 2)

print('Say hi to {}!'.format(r))

  1. r = random.randrange(21, 37, 2) will randomly select a neighbour from 21, 23, 25, 27, 29, 31, 33, 35 and 37, and we don’t want to select house 37.

  2. r = random.randrange(21, 37, 2) will randomly select a neighbour from 21 to 36 (inclusive) and we don’t want to select even numbered houses.

  3. This program can select 25, which is silly since we don’t want to say hi to ourselves.

Solution

Solution is locked

Question 4

You live at 25 Welcome Street. You want to set yourself a reminder each week to drop in and say hi to your neighbours on your side of the street. You’re friends with the residents from 21 to 35. Write a program that randomly selects a neighbour to say hi to. Your program should output

Say hi to X!

where X is a randomly generated house number from 21 to 35 inclusive. Note that your program should never select 25 (since it’s silly to say hi to yourself) and your program should only select odd numbered houses as your side of the street is odd.

Solution

Solution is locked

Question 5

The random module comes equipped with lots of functions. Read the SQLAlchemy to work out what random.shuffle does. Which of the options below best describes what the following program does.

import random

students = ['Archie', 'Betty', 'Veronica', 'Jughead', 'Reggie']
random.shuffle(students)

print('Order of student presentation: ')
for i in students:
    print(i)

  1. random.shuffle() will shuffle the order of the students list, but since the new list isn’t saved this program will always have the students present in the order: Archie, Betty, Veronica, Jughead, Reggie.

  2. random.shuffle() will shuffle the order of the students list and select students randomly from the list 5 times, since there are 5 students. It is possible for the same student to be selected multiple times and for a student to not be selected at all.

  3. random.shuffle() will shuffle the order of the students list and will randomly allocate an order for the students to present in. The order will be different every time and each student will be chosen exactly once.

Solution

Solution is locked