Chapter 9: Weight Converter Program¶

🚀 Open Notebook¶

📺 Video Tutorial¶

Python weight conversion exercise 🏋️ (5:47)

📚 What You’ll Learn¶

Create a practical unit converter that switches between pounds and kilograms!

🎯 Learning Objectives¶

Work with unit conversions
Use conversion factors in calculations
Format decimal output
Create practical, real-world programs
Understand metric vs imperial measurements

📖 Concept Explanation¶

Weight Units¶

Pounds (lbs): Imperial/US measurement system
Kilograms (kg): Metric measurement system (used in most of the world)

Conversion Formula¶

1 kilogram = 2.20462 pounds
1 pound = 0.453592 kilograms

Or using grams:
1 kg = 1000 grams
1 lb = 453.6 grams
Therefore: 1 kg ≈ 2.2046 lbs

How the Program Works¶

Ask for weight value
Ask for current unit (L or K)
Calculate conversion factor
Convert to opposite unit
Display result

💡 Examples¶

Example 1: Pounds to Kilograms¶

Input: 150 pounds
Calculation: 150 / 2.20462 = 68.04 kg
Output: "Your weight in Kgs: 68.04"

Example 2: Kilograms to Pounds¶

Input: 70 kilograms
Calculation: 70 * 2.20462 = 154.32 lbs
Output: "Your weight in Lbs: 154.32"

✍️ Practice Exercises¶

Exercise 1: Add Rounding Options¶

# Ask user how many decimal places they want
decimal_places = int(input("Decimal places: "))
print(f"Weight: {weight:.{decimal_places}f}")

Exercise 2: Improve User Interface¶

print("=== Weight Converter ===")
print("L - Convert from Pounds to Kilograms")
print("K - Convert from Kilograms to Pounds")
choice = input("Select option: ")

Exercise 3: Add More Weight Units¶

Add conversions for:

Ounces (oz): 1 lb = 16 oz
Stones (st): 1 stone = 14 lbs (used in UK)
Grams (g): 1 kg = 1000 g

Exercise 4: Bidirectional Converter¶

# Let user choose which direction:
# 1. lbs to kg
# 2. kg to lbs

🔍 Code Analysis¶

Using .upper()¶

unit = input("Enter L or K: ")
if unit.upper() == "L":  # Accepts both 'l' and 'L'
    # convert...

This makes the program more user-friendly!

Formatting Output¶

# Without formatting:
print(f"Weight: {weight}")  # 68.039215686274506

# With formatting (2 decimal places):
print(f"Weight: {weight:.2f}")  # 68.04

🎮 Enhanced Weight Converter¶

def weight_converter():
    """Convert between pounds and kilograms"""
    
    print("=" * 40)
    print("     WEIGHT CONVERTER")
    print("=" * 40)
    
    # Get weight
    try:
        weight = float(input("\nEnter weight value: "))
        if weight <= 0:
            print("Error: Weight must be positive!")
            return
    except ValueError:
        print("Error: Please enter a valid number!")
        return
    
    # Get unit
    print("\nSelect unit:")
    print("L - Pounds (lbs)")
    print("K - Kilograms (kg)")
    unit = input("Your choice (L/K): ").upper()
    
    # Conversion factor
    LBS_TO_KG = 0.453592
    KG_TO_LBS = 2.20462
    
    # Convert and display
    if unit == "L":
        converted = weight * LBS_TO_KG
        print(f"\n{weight} lbs = {converted:.2f} kg")
    elif unit == "K":
        converted = weight * KG_TO_LBS
        print(f"\n{weight} kg = {converted:.2f} lbs")
    else:
        print("Error: Invalid unit!")
    
    print("=" * 40)

# Run converter
weight_converter()

📝 Common Weight Conversions¶

Pounds (lbs)	Kilograms (kg)
1	0.45
10	4.54
50	22.68
100	45.36
150	68.04
200	90.72

🌍 Real-World Applications¶

Fitness & Health¶

# BMI Calculator with weight conversion
height_m = float(input("Height in meters: "))
weight_kg = float(input("Weight in kg: "))
bmi = weight_kg / (height_m ** 2)
print(f"BMI: {bmi:.1f}")

Travel¶

# Luggage weight checker
weight_lbs = float(input("Luggage weight (lbs): "))
weight_kg = weight_lbs * 0.453592

if weight_kg > 23:  # Standard airline limit
    print(f"Overweight! {weight_kg:.1f} kg exceeds 23 kg limit")
else:
    print(f"Within limit: {weight_kg:.1f} kg")

🚀 Challenge Projects¶

Challenge 1: Multi-Unit Converter¶

Create a converter for:

Weight (lbs, kg, oz, stones)
Length (miles, km, feet, meters)
Temperature (C, F, K)
Volume (gallons, liters)

Challenge 2: Batch Converter¶

# Convert multiple weights at once
weights = [120, 150, 180, 200]
for weight in weights:
    kg = weight * 0.453592
    print(f"{weight} lbs = {kg:.2f} kg")

Challenge 3: Conversion Table Generator¶

# Generate a conversion table
print("LBS | KG")
print("-" * 15)
for lbs in range(10, 210, 10):
    kg = lbs * 0.453592
    print(f"{lbs:3d} | {kg:6.2f}")

🎓 Key Takeaways from Video¶

Variables store data values that can be reused
Use if-elif-else for conditional logic
Follow along with the video for hands-on practice

💡 These points cover the main concepts from the video tutorial to help reinforce your learning.

🔗 Next Chapter¶

Continue to Chapter 10: Temperature Converter to create another conversion program!