Learn Python

1 Why Functions? 🤔

💡Problem: Writing the same code over and over = boring and messy!

# WITHOUT functions (repetitive!)
print("Hello, Alice!")
print("Welcome!")
print("---")

print("Hello, Bob!")
print("Welcome!")
print("---")

print("Hello, Charlie!")
print("Welcome!")

print("===")

# WITH functions (clean!)
def greet(name):
    print("Hello,", name + "!")
    print("Welcome!")
    print("---")

greet("Alice")
greet("Bob")
greet("Charlie")

✨Magic! Functions let you write code ONCE and reuse it many times!

2 Creating Your First Function 📦

📚Learn: Use def to define a function!

def function_name(parameters):

↓

code block (indented)

↓

function_name(arguments)

# Define a simple function
def say_hello():
    print("Hello, World!")
    print("Functions are cool!")

# Call the function
say_hello()
print("---")
say_hello()
print("---")

# Another function
def celebrate():
    print("🎉 Party time!")
    print("🎊 Celebration!")

celebrate()

🔑Key parts: def keyword, name, parentheses (), colon :, indented code!

3 Functions with Parameters 📥

🎯Learn: Parameters let functions accept input!

# Function with one parameter
def greet(name):
    print("Hi", name + "!")

greet("Alice")
greet("Bob")

print("---")

# Function with multiple parameters
def introduce(name, age):
    print("My name is", name)
    print("I am", age, "years old")

introduce("Alice", 15)
print("---")
introduce("Bob", 16)

💡Tip: Parameters are like variables that get their values when you call the function!

4 Return Values 📤

🔄Learn: Functions can send values back with return!

# Function that returns a value
def add(a, b):
    result = a + b
    return result

# Use the returned value
sum1 = add(5, 3)
print("5 + 3 =", sum1)

sum2 = add(10, 20)
print("10 + 20 =", sum2)

print("---")

# Multiple operations
def multiply(a, b):
    return a * b

def divide(a, b):
    return a / b

print("4 * 5 =", multiply(4, 5))
print("20 / 4 =", divide(20, 4))

🎁Think: return is like the function giving you a gift back!

5 Temperature Converter! 🌡️

🔥Build: Create temperature conversion functions!

# Celsius to Fahrenheit
def c_to_f(celsius):
    fahrenheit = (celsius * 9/5) + 32
    return fahrenheit

# Fahrenheit to Celsius
def f_to_c(fahrenheit):
    celsius = (fahrenheit - 32) * 5/9
    return celsius

# Test the functions
temp_c = input("Enter temperature in Celsius: ")
temp_c = int(temp_c)

temp_f = c_to_f(temp_c)
print(temp_c, "°C =", temp_f, "°F")

print("---")

temp_f2 = input("Enter temperature in Fahrenheit: ")
temp_f2 = int(temp_f2)

temp_c2 = f_to_c(temp_f2)
print(temp_f2, "°F =", round(temp_c2, 1), "°C")

🌟Try: 0°C = 32°F, 100°C = 212°F, 32°F = 0°C!

6 Grade Calculator! 📝

🎓Final Project: Build a grade calculator with functions!

# Function to get letter grade
def get_grade(score):
    if score >= 90:
        return "A"
    elif score >= 80:
        return "B"
    elif score >= 70:
        return "C"
    elif score >= 60:
        return "D"
    else:
        return "F"

# Function to check if passing
def is_passing(score):
    return score >= 60

# Main program
print("=== GRADE CALCULATOR ===")

score1 = input("Enter score 1: ")
score1 = int(score1)

score2 = input("Enter score 2: ")
score2 = int(score2)

score3 = input("Enter score 3: ")
score3 = int(score3)

# Calculate average
average = (score1 + score2 + score3) / 3

print("---")
print("Score 1:", score1, "- Grade:", get_grade(score1))
print("Score 2:", score2, "- Grade:", get_grade(score2))
print("Score 3:", score3, "- Grade:", get_grade(score3))
print("---")
print("Average:", round(average, 1))
print("Final Grade:", get_grade(average))

if is_passing(average):
    print("✅ PASSING!")
else:
    print("❌ Need to improve")

🎯Try: 95, 87, 92 for good grades! Or 55, 60, 58 to test failing!

🎯 Python Functions - Day 5

1 Why Functions? 🤔

2 Creating Your First Function 📦

3 Functions with Parameters 📥

4 Return Values 📤

5 Temperature Converter! 🌡️

6 Grade Calculator! 📝

🎉 You're a Function Expert! 🎉