Python Functions

Python Functions

Python functions are blocks of code that are only run when called. Data known as parameters can be passed into a function and data can be returned as the result of a function. When using decomposition to break a problem down into smaller, easier parts functions can be used to handle seperate parts of the problem.


Task: The program has two functions. The first function is used to add numbers, the second is used to subtract. Depending on what option the user picks a different function is called.

  • Run the code to check it works.
  • Improve the model by creating two new functions to allow numbers to be divided and multiplied.
  • Add # comments to explain what your code does.
  • Add screenshots of the code to your notes in powerpoint.
  • Can you develop the model further to calculate squared numbers, cubed numbers and square roots?




# This function adds two numbers
def add(x, y):
   return x + y
# This function subtracts two numbers
def subtract(x, y):
   return x - y

print("Select operation.")
print("1.Add function")
print("2.Subtract function")

choice = input("Enter choice(1 or 2): ")
num1 = float(input("Enter first number: "))
num2 = float(input("Enter second number: "))

if choice == '1':
   print(num1,"+",num2,"=", add(num1,num2))
elif choice == '2':
   print(num1,"-",num2,"=", subtract(num1,num2))
   print("Invalid input")


Default values can be added to functions that will return a default value. See below.....


def my_function(country = "Norway"):
  print("I am from " + country)



Create a function similar to the one above with a default value of 'Parker' that states what school you go to.


The code below uses a function to draw a square using turtle. See if you can develop this code so that the user can select different shapes to draw. Depending on the option chosen python should run a different function.

import turtle

def draw_square(t, sz):
   """Make turtle t draw a square of sz."""
   for i in range(4):

wn = turtle.Screen()       
wn.title("Turtle using functions")

a = turtle.Turtle()      
draw_square(a, 50)