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Lesson 1

Lesson 1 of 34

Functions

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Code Example

# function with simple output
def shout():
    print("WATCH OUT!")

# function with simple output
def show_line():
    print("**********")

Instructions

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A function is like a recipe that stores a set of instructions for Python to follow later.
We start by using the word def, which is short for "define."
Inside the function, we indent the code to show it belongs to that specific recipe.
The function won't do anything until you call its name, like shout().
This helps us reuse the same code over and over without having to type it all out again.

Code Example

# simple function with a return
def show_color(color):
    print("Your favorite color is", color)

show_color("Blue")

# simple function with a return
def add_ten(number):
    print(number + 10)

add_ten(5)

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A function is a small group of code that does a job for us.
We make a function using the word def and give it a name.
The word inside the parentheses (like color or number) is what we give to the function.
Inside the function, print() shows a message on the screen.
To use a function, we write its name with something inside the parentheses, like show_color("Blue").

Code Example

# Function to show an item and its price
def buy_item(item, price=5.0):
    print("Item:", item, "| Price:", price)

buy_item("Book")
buy_item("Phone", 500.0)

# Function to print a message from a specific user
def send_msg(text, user="Guest"):
    print(user, "says:", text)

send_msg("Hello!")
send_msg("I am late", "Sam")

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Think of a function like a machine that can take in different pieces of information to do a job.
Sometimes, we give a piece of information a "backup value" using the equals sign, like price=5.0.
This backup value is used automatically if you don't pick a specific one yourself.
If you do provide your own value, Python will use yours instead of the backup.
This is really helpful because it saves you time when most of your answers are the same!

Code Example

# Function to return both the sum and difference of two numbers
def get_math(a, b):
    return a + b, a - b

total, diff = get_math(10, 5)
print(total, diff)

# Function to return the first and last name from a list
def split_name(full_name):
    first = full_name[0]
    last = full_name[1]
    return first, last

fname, lname = split_name(["Sam", "Smith"])
print(fname, lname)

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A function can send back more than one answer at the same time.
We use return to send answers back from the function.
When a function sends back two answers, we can save them into two names, like total and diff.
We can also pull out pieces from a list, like the first and last name.
print() shows the answers on the screen so we can see them.

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Functions

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Lesson 1 of 34

Next: DocStrings →

# simple function with a return def show_color(color): print("Your favorite color is", color) show_color("Blue") # simple function with a return def add_ten(number): print(number + 10) add_ten(5)

# Function to show an item and its price def buy_item(item, price=5.0): print("Item:", item, "| Price:", price) buy_item("Book") buy_item("Phone", 500.0) # Function to print a message from a specific user def send_msg(text, user="Guest"): print(user, "says:", text) send_msg("Hello!") send_msg("I am late", "Sam")

# Function to return both the sum and difference of two numbers def get_math(a, b): return a + b, a - b total, diff = get_math(10, 5) print(total, diff) # Function to return the first and last name from a list def split_name(full_name): first = full_name[0] last = full_name[1] return first, last fname, lname = split_name(["Sam", "Smith"]) print(fname, lname)