Subroutines: Procedures

Name a block of code so you can reuse it.

A subroutine is a named block of code you can run whenever you like. A procedure is a subroutine that does a job but does not send a value back.

Defining and calling a procedure

hello.py

def say_hello():
    print("Hello!")
    print("Welcome to the program.")

say_hello()
say_hello()

Output

Hello!
Welcome to the program.
Hello!
Welcome to the program.

How it works

def creates a subroutine and gives it a name.
The indented lines are the body — they do not run until the subroutine is called.
say_hello() calls it; we call it twice, so the body runs twice.

welcome.py

def welcome(name):
    print("Hello", name)
    print("Good to see you")

welcome("Ava")
welcome("Ben")

Output

Hello Ava
Good to see you
Hello Ben
Good to see you

How it works

name inside the brackets is a parameter — a box that receives a value when the procedure is called.
welcome("Ava") sends "Ava" into name for that run.
The same procedure does its job with different data each time.

area.py

def show_area(width, height):
    area = width * height
    print("Area is", area)

show_area(4, 5)
show_area(3, 7)

Output

Area is 20
Area is 21

How it works

A procedure can take several parameters, separated by commas.
The values are matched to the parameters in order: 4 goes to width, 5 to height.

A procedure does a jobIt may take parameters, but it does not return a value.