1.6 Random Numbers

When we talk about random numbers and probability, we usually mean a number between 0.0 to <1.0.

0.0 is the event never happening, and 0.999 is the event happening.

Generating random numbers with a computer is complex. Programming languages usually have a library function which will seed the random number generator for you. Python handles this with the random module.

Python, like all programming languages will generate random numbers.

Problem: Generate a random number with Python

import random

print(random.random())

That might give you a number like:

0.10940338745940381

or

0.7921996495976178

or

0.5752671510235025

or

0.04780427949110977

or

0.9540278243078905

or

0.22425650016401177

or

0.866212373677892

or

0.683149562597131

or

0.7007903302436131

or perhaps something truly useful like,

8.010696446425492e-05

As you can see, the random() will only generate a number between 0.0 and 1.0. These numbers don't fit on the face of a die, nor do they help you when you want to play a game of 'guess a number from 1 to 10'.

Problem: Generate a series of numbers from 1 to 10 in a human legible form

import random

for i in range(1,11):

    print(i, random.randint(1,10), random.random())

My output and your output should be different. Here's mine:

1 3 0.24326554564589864

2 1 0.18308787873100463

3 5 0.7207806043918445

4 9 0.0973342135948797

5 9 0.593122826395729

6 5 0.3597623960977868

7 9 0.8817712957458808

8 7 0.5897880781225155

9 5 0.09039521721782362

10 10 0.5453265930448745

What are we looking at? The first column is the iteration of the loop. The second column is the random number that Python generated. It was generated by using random.randint(). The third column is the random number generated by random.random().

Clearly, a number generated by random.randint() will fit on a face of a die and work well in a game of 'guess a number from 1 to 10'.

Problem: Generate a series of numbers from 1 to 10 in a human legible form

import random

for i in range(1,11):

    print(random.randint(1,10))

This was my output, what was yours?

5

7

1

3

4

10

3

8

8

4

>>>

Interesting things from the API

Python has some interesting functions built into the random module. My favourites are random.choice(), random.shuffle() and random.sample().

choice()

import random

print(random.choice('abcdefghijklmnopqrstuvwxyz'))

OUTPUT: h

Remember that list called caf_specials that we used in the loop unit? I told you not to worry about what a list was. Let's use the list again in my shuffle() example, and continue to not worry about it.

shuffle()

import random

caf_specials = [ 'breakfast sandwich', 'milk', 'rice', 'pizza', 'salad', 'fish and chips' ]

random.shuffle(caf_specials)

print(caf_specials)

OUTPUT: ['salad', 'pizza', 'milk', 'fish and chips', 'breakfast sandwich', 'rice']

Let's reuse the caf_specials list, one more time. Don't worry about how it works!

sample()

import random

caf_specials = [ 'breakfast sandwich', 'milk', 'rice', 'pizza', 'salad', 'fish and chips' ]

print (random.sample(caf_specials, 3))

OUTPUT:  ['rice', 'fish and chips', 'salad']

Looking at Random numbers another way: TURTLE

import turtle #import the turtle module

import random #import the random module

myColours = ['orange', 'yellow', 'green', 'blue', 'black', 'purple', 'red'] #a list of strings

bob = turtle.Turtle() #create a turtle named bob

bob.goto(55, 75) #move bob to x55 and y75

#let's add some random values

bob.goto(random.randint(0,255), random.randint(0,255)) #generate a random x and y

for x in range(0,5):

  bob.goto(random.randint(0,255), random.randint(0,255))  #generate a random x and y 4 times

for x in range(0,15):

  bob.goto(random.randint(0,255), random.randint(0,255))  #generate a random x and y each time the loop happens

  randomColour= random.choice(myColours)        #use random.choice to make a random selection from myColours list 

  bob.pencolor(randomColour)                    #set the pen to that random myColours

import turtle #import the turtle module

import random #import the random module

myColours = ['orange', 'yellow', 'green', 'blue', 'black', 'purple', 'red'] #a list of strings

bob = turtle.Turtle() #create a turtle named bob

for x in range(0,200):

  bob.penup()

  bob.goto(random.randint(-255,255), random.randint(-255,255))

  bob.pendown()

  randomColour= random.choice(myColours)  

  bob.pencolor(randomColour)      

  bob.dot()   #try it like this, then comment this line and uncomment the next line

  #bob.dot(random.randint(1,100)) #what happens to the dot size?