</> 13-functions.py

python-for-j277 / subroutines · Lesson 13

Lesson 13 — Subroutines

Subroutines: Functions

Subroutines that send a value back.

A function is a subroutine that works out an answer and returns it. You can store or use that answer however you like.

Returning a value

double.py

def double(number):
    return number * 2

result = double(6)
print(result)
print(double(10))

Output

12
20

How it works

return sends a value back to wherever the function was called.
double(6) works out 12 and hands it back; we store it in result.
You can also use the returned value straight away, like printing double(10).

A function that builds an answer

area.py

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

print("Area:", area(4, 5))
total = area(2, 3) + area(4, 5)
print("Total:", total)

Output

Area: 20
Total: 26

How it works

This function returns the area instead of printing it.
Because it returns a value, you can use it inside other calculations.
area(2, 3) + area(4, 5) adds the two returned answers together.

Procedure or function?

	Procedure	Function
Does	Carries out a task	Works out and returns a value
Sends back	Nothing	A value, using `return`
Used like	`show_area(4, 5)`	`total = area(4, 5)`

return ends itOnce return runs, the function stops immediately — any lines after it are skipped.

The deciding questionIf a subroutine gives you an answer back with return, it is a function. If it just does a job, it is a procedure.

What you have learned

A function returns a value with return.
The returned value can be stored or used inside an expression.
return ends the function straight away.
Functions return a value; procedures do not.