Python Explained for Absolute Beginners — What It Is, Why It Matters and How to Write Your First Real Program

# This is your first Python program.
# Lines starting with '#' are comments — Python ignores them.
# They exist purely to explain your code to humans (including future-you).

# The print() function outputs text to the screen.
# Whatever you put inside the parentheses gets displayed.
print("Hello, World! I just ran my first Python program.")

# Python can do maths instantly — no setup needed
print("The answer to 42 multiplied by 7 is:", 42 * 7)

# You can store a value in a variable and use it later
your_name = "Alex"  # This creates a variable called 'your_name'
print("Welcome to Python,", your_name)  # Python slots the value in automatically

# ── STRINGS: text wrapped in quotes ──────────────────────────────────
product_name = "Wireless Headphones"   # double quotes work
category = 'Electronics'               # single quotes also work — same result

# ── INTEGERS: whole numbers, no decimal point ─────────────────────────
stock_quantity = 142
warehouse_shelf = 7

# ── FLOATS: numbers with a decimal point ──────────────────────────────
product_price = 89.99
tax_rate = 0.08    # 8% sales tax stored as a decimal

# ── BOOLEANS: only two possible values — True or False ───────────────
is_in_stock = True
is_on_sale = False

# ── type() tells you what data type Python sees ───────────────────────
print("Product:", product_name)
print("Price: $", product_price)
print("Stock:", stock_quantity, "units")
print("In stock?", is_in_stock)
print()

# Python can calculate and format output in one line
total_price = product_price * (1 + tax_rate)   # price + 8% tax
print("Total price with tax: $", round(total_price, 2))  # round to 2 decimal places

# type() is your X-ray vision — use it when you're unsure
print()
print("Data type of product_name:", type(product_name))
print("Data type of product_price:", type(product_price))
print("Data type of stock_quantity:", type(stock_quantity))
print("Data type of is_in_stock:", type(is_in_stock))

# A simple coffee shop ordering system
# This demonstrates if / elif / else decision-making

customer_age = 16           # the customer's age
customer_balance = 12.50    # money in their account (dollars)
coffee_price = 4.75         # cost of a large coffee
minimum_age = 18            # age required to order espresso-based drinks

print("=== Coffee Shop Order System ===")
print(f"Customer age: {customer_age}")
print(f"Account balance: ${customer_balance}")
print(f"Coffee price: ${coffee_price}")
print()

# FIRST DECISION: Is the customer old enough?
if customer_age >= minimum_age:
    print("Age check: PASSED — customer can order espresso drinks.")

    # NESTED DECISION: Can they actually afford it?
    # This if/else only runs if the age check passed
    if customer_balance >= coffee_price:
        remaining_balance = customer_balance - coffee_price
        print("Payment: APPROVED")
        print(f"Enjoy your coffee! Remaining balance: ${remaining_balance:.2f}")
    else:
        # :.2f formats the number to exactly 2 decimal places
        shortfall = coffee_price - customer_balance
        print(f"Payment: DECLINED — you need ${shortfall:.2f} more.")

elif customer_age >= 13:
    # elif = 'else if' — checks a second condition when the first was False
    print("Age check: PARTIAL — you're a teen! You can order cold brew or frappes.")

else:
    # This runs if ALL conditions above were False
    print("Age check: FAILED — sorry, espresso drinks are for adults only.")
    print("Can we offer you a hot chocolate instead?")

# ── BMI Calculator ────────────────────────────────────────────────────
# This program asks the user for their height and weight,
# calculates their Body Mass Index (BMI), and gives a health category.
# BMI Formula: weight (kg) divided by height (m) squared

print("==============================")
print("   Python BMI Calculator")
print("==============================")
print()

# input() always returns a STRING — we must convert to float for maths
height_input = input("Enter your height in metres (e.g. 1.75): ")
weight_input = input("Enter your weight in kilograms (e.g. 70): ")

# Convert the string inputs to floating-point numbers
height_in_metres = float(height_input)   # e.g. '1.75' becomes 1.75
weight_in_kg = float(weight_input)       # e.g. '70' becomes 70.0

# Calculate BMI: weight divided by height squared
bmi = weight_in_kg / (height_in_metres ** 2)   # ** means 'to the power of'
bmi_rounded = round(bmi, 1)   # round to 1 decimal place for readability

print()
print(f"Your BMI is: {bmi_rounded}")
print()

# Categorise the BMI result using if/elif/else
if bmi < 18.5:
    category = "Underweight"
    advice = "Consider speaking to a nutritionist about healthy weight gain."
elif bmi < 25.0:
    category = "Normal weight"      # The healthy range
    advice = "Great work — keep maintaining your healthy lifestyle!"
elif bmi < 30.0:
    category = "Overweight"
    advice = "Regular exercise and a balanced diet can help."
else:
    category = "Obese"
    advice = "Please consult a healthcare professional for personalised guidance."

print(f"Category: {category}")
print(f"Advice:   {advice}")
print()
print("Note: BMI is a general guide only, not a medical diagnosis.")