Procedures and abstraction

What we'll do

• A procedure is a named block of code you can use again and again.
• In Python a procedure is made with def.
• This is part of Big Idea 3: building programs from reusable parts.

Make a procedure

• Start with def, then a name, then ().
• Put the code indented below.
• Call the procedure by writing its name with ().

def greet():
    print("Hello!")

greet()
greet()

Parameters pass data in

• A parameter is a value the procedure receives.
• Put the parameter name inside the ().
• Inside the procedure you use it like a variable.

def greet(name):
    print("Hello, " + name)

greet("Mia")
greet("Sam")

return gives a value back

• return sends a value out of the procedure.
• The caller can store that value or use it.
• After return, the procedure stops.

def square(n):
    return n * n

answer = square(5)
print(answer)

Why procedures help: abstraction

• Abstraction means hiding the details behind a simple name.
• You call square(5) and do not think about how it works inside.
• This makes code shorter, clearer, and easy to reuse.

In AP CSP pseudocode

• The exam uses a pseudocode for procedures.
• PROCEDURE is like def; RETURN is like return.

PROCEDURE square(n)
{
    RETURN(n * n)
}

Common mistakes

• A procedure with a return gives back a value; call it with ().
• Abstraction hides the detail behind a simple name.

Now you try

• Read each task to see the procedure name and what it must return.
• Press Check answer to test your code.