def hello():

print("Hello!")

hello()

# -- Defining vs. calling --

# It's still all sequential!

def user_age_in_seconds():

user_age = int(input("Enter your age: "))

age_seconds = user_age * 365 * 24 * 60 * 60

print(f"Your age in seconds is {age_seconds}.")

print("Welcome to the age in seconds program!")

user_age_in_seconds()

print("Goodbye!")

# -- Don't reuse names --

def print():

print("Hello, world!") # Error!

# -- Don't reuse names, it's generally confusing! --

friends = ["Rolf", "Bob"]

def add_friend():

friend_name = input("Enter your friend name: ")

friends = friends + [friend_name] # Another way of adding to a list!

add_friend()

print(friends) # Always ['Rolf', 'Bob']

# -- Can't call a function before defining it --

say_hello()

def say_hello():

print("Hello!")

# -- Remember function body only runs when the function is called --

def add_friend():

friends.append("Rolf")

friends = []

add_friend()

print(friends) # [Rolf]