1. Random Numbers In today’s lesson we will look at:
why we might want a random number
whether they really are random
how to create and scale random numbers in Python

2. Why Random Numbers? Random things are unpredictable
You might want to add randomness to a program so that it doesn’t behave in the same way every time.
Some people think that randomness makes things seem more “real” or “human” – e.g. making things wobbly.
You might want to simulate or model an actual random event – e.g. a dice throw

3. Examples A tree drawn in Scratch using recursion
The same program with added randomness

4. Can a Computer Do That?
Random numbers are unpredictable, but computers always follow rules
A computer can’t really create random numbers – it uses rules to create pseudo-random numbers
The computer might use all sorts of variables that change – e.g. the time – to help it create numbers that appear to be random.

5. Programming Randomness
Most programming languages (and also spreadsheets and other applications) only give you a number from 0 to 1.
In BASIC, for example, the following program would print a random number:
X = RND(1)
PRINT X
Excel is very similar. Python doesn’t work like that, though.

6. Python Example
The first thing you need to do is import the random library using the following code: from random import randint
You can then use the randint() function, e.g. to simulate the roll of a die you could use: die = randint(1,6)
That would give you a random integer from 1 to 6

7. Random Things
What happens if you want a random thing that isn’t a number, for example a random day, or a random person from your class?
You can number the days, people, etc., and put their names into a list or tuple.
You can then produce a random number and use that as the index to look up the name.

8. Example? To give a random day of the week: from random import randint
day = ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
for i in range(10):
print(day[randint(0,6)])

9. Distribution
All of the examples so far produce random numbers with a linear distribution – i.e. they should be spread evenly throughout the chosen range.
What about if you wanted it to be more likely that you’d get a small number (or a large one)?
Think about square numbers – 1, 2, 4, 9, 16, 25, 36, 49, 64, 81, 100, etc. – how are they spaced?
You can change the distribution of random numbers by raising them to a power.