Magic Boxes, Functions

So far, we have been giving commands line by line. But what if you have a group of commands you use often? Typing them every time would be annoying.

That is when you use a function. A function is like a magic box that bundles a set of commands.

Creating a function (def)

To create a function, we use def, short for “define.”

Type this in PyCharm.

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

# Use the function (call it)
say_hello()

In plain English:

Define a magic box named say_hello:
    print "Hello!"
    print "Welcome to the Python course."

(Definition ends)

Now open the say_hello box (use it)!

Once you create the box, just writing say_hello() runs everything inside it.

Functions with ingredients (parameters)

Like a vending machine that gives you a drink when you insert a coin, you can also pass ingredients into a function.

def greet(name):
    print("Nice to meet you,", name, "!")

greet("Alex")
greet("Python")

Translation:

Define a magic box called greet (the ingredient is called name):
    print "Nice to meet you," plus name plus "!"

(Definition ends)

Use the greet box (ingredient is "Alex")
Use the greet box (ingredient is "Python")

Result:

Nice to meet you, Alex !
Nice to meet you, Python !

Functions that return a result (return)

A magic box can finish its work and hand you back a result. That is what return is for.

def add(a, b):
    return a + b

result = add(10, 20)
print("Result:", result)

Translation:

Define a magic box called add (ingredients are a and b):
    return the sum of a and b

(Definition ends)

Put 10 and 20 into the add box, and remember the result as result
Print result

Why use functions?

They save effort: You do not need to write the same code again and again.
They keep code tidy: Long code can be tucked into a box with a name.
They are easy to change: Edit the box once, and everything that uses it updates.

Now you are a creator of your own magic boxes!