random (slides)

CSC 110 – Generating Random Numbers and Other Important Functions and Methods

random module

We need to import the module random

What do the functions .random() and .randint() return?

import random

n = random.random() #returns a random float between 0 and 1
print(n)

n = random.randint(0, 9) #returns a random integer betweem 0 and 9.


print(n)

0.8734221981946652
5

Write a function

1. Function name is pick_winner
2. It takes a list as argument
3. It generates a random index, and returns the item at that position

winner = pick_winner(["Peter", "Joan", "Mary", "June"])
print(winner)

Write a function – solution

import random

def pick_winner(names):
  index = random.randint(0, len(names) - 1)
  return names[index]

if __name__ == "__main__":
  winner = pick_winner(["Peter", "Joan", "Mary", "June"])
  print(winner)

Joan

Setting a seed

What happens when you run pick_winner multiple times?

To get always the same result (for autograding purposes, for example) we can set a seed.

import random

def pick_winner(names):
  random.seed(123)
  index = random.randint(0, len(names) - 1)
  return names[index]

if __name__ == "__main__":
  winner = pick_winner(["Peter", "Joan", "Mary", "June"])
  print(winner)

Peter

Write a function

Write a function random_list that takes as argument a list of numbers. Iterate over each list element (with a while loop), replacing each integer with a random number between zero and the original number. Set the seed as 123 in your function.

Name your file random_list.py and submit to Gradescope.

# test case
assert random_list([3, 2, 1, 3, 5]) == [0, 1, 0, 3, 2]

Write a function – solution

import random

def random_list(numbers):
  random.seed(123)
  index = 0
  while index < len(numbers):
    item = numbers[index]
    numbers[index] = random.randint(0, item)
    index += 1
  return numbers

if __name__ == "__main__":
  assert random_list([3, 2, 1, 3, 5]) == [0, 1, 0, 3, 2]
  print("pass the test")

pass the test