Learn > Higher Computing Science > 7. Functions

Functions

A function is very similar to a procedure. Both are blocks of code that do a specific job. The main difference is:

  • A procedure performs some steps
  • A function performs some steps and then sends a value(s) back to where it was called

We do this using the return statement.

Example

def calculate_area(width, height):
    area = width * height
    return area
  • The function is called calculate_area.
  • It takes two parameters: width and height.
  • It multiplies them to work out the area.
  • The return line sends the result back.

How return works

When Python reaches the return statement:

  • That value after return is sent back to where the function was called
  • The function then ends immediately – no more lines in the function are run after return

This means you can store the result in a variable, or use it in another calculation.

Function design

  • Parameters pass data into a subprogram.
  • Return passes data out of a subprogram.

Comparing Rectangle Area

  1. Calculate area of rectangle 1
  2. Calculate area of rectangle 2
  3. Compare area of rectangles
1 Calculate area of rectangle 1 IN width, height
OUT area
2

Calculate area of rectangle 2

 

 IN width, height
OUT area
3

Compare area of rectangles

 

 IN area1, area2
OUT
1.1 area = width * height
1.2 return area
2.1 if area1 > area2
2.2         display “Area 1 is bigger”
2.3  else
2.4         display “area 2 is bigger”

 

def calc_area(width, height):
    area = width * height
    return area

def compare_areas(area1, area2):
    if area1 > area2:
        print("Area 1 is bigger")
    else:
        print("Area 2 is bigger")

# Main
area1 = calc_area(10,20)
area2 = calc_area(5,10)

compare_areas(area1, area2)