Python Loops: How to Automate Repetitive Tasks Like a Pro

# ❌ The tedious way
print(1)
print(2)
print(3)
print(4)
print(5)

# ✅ The loop way
for number in range(1, 6):
    print(number)

# Count from 0 to 4
for i in range(5):
    print(f"Count: {i}")

# Output:
# Count: 0
# Count: 1
# Count: 2
# Count: 3
# Count: 4
🔍 Range Explained:

range(5) = 0, 1, 2, 3, 4

range(1, 6) = 1, 2, 3, 4, 5

range(1, 10, 2) = 1, 3, 5, 7, 9 (steps of 2)

Real-World Example: Daily Reminders
python
# Set up daily reminders
tasks = ["Drink water", "Take break", "Check posture", "Stretch"]

print("📋 Your daily reminders:")
for task in tasks:
    print(f"• {task}")

# Output:
# 📋 Your daily reminders:
# • Drink water
# • Take break
# • Check posture
# • Stretch

# Countdown timer
countdown = 5

while countdown > 0:
    print(f"🚀 {countdown}...")
    countdown -= 1  # Don't forget this!

print("Blast off! 🎉")

# Output:
# 🚀 5...
# 🚀 4...
# 🚀 3...
# 🚀 2...
# 🚀 1...
# Blast off! 🎉

# ❌ DANGER: Infinite loop!
# countdown = 5
# while countdown > 0:
#     print("This will run forever!")
# 🛑 Always update your condition!
Real-World Example: User Input Validation
python
# Keep asking until we get valid input
age = None

while age is None:
    try:
        user_input = input("How old are you? ")
        age = int(user_input)
        
        if age <= 0:
            print("Please enter a valid age!")
            age = None
    except ValueError:
        print("That's not a number! Try again.")

print(f"Great! You are {age} years old.")

# Search for a number, stop when found
numbers = [3, 7, 2, 9, 4, 6]
target = 9

for number in numbers:
    print(f"Checking {number}...")
    if number == target:
        print("🎯 Found it!")
        break  # Exit the loop immediately
    print("Not this one...")

# Output:
# Checking 3...
# Not this one...
# Checking 7...
# Not this one...
# Checking 2...
# Not this one...
# Checking 9...
# 🎯 Found it!

# Print only even numbers
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

print("Even numbers:")
for num in numbers:
    if num % 2 != 0:  # If number is odd
        continue      # Skip to next iteration
    print(num)

# Output:
# Even numbers:
# 2
# 4
# 6
# 8
# 10

import random

def guessing_game():
    secret_number = random.randint(1, 100)
    attempts = 0
    max_attempts = 7
    
    print("🎮 Welcome to the Number Guessing Game!")
    print(f"I'm thinking of a number between 1 and 100.")
    print(f"You have {max_attempts} attempts to guess it!")
    
    while attempts < max_attempts:
        try:
            guess = int(input(f"\nAttempt {attempts + 1}/{max_attempts}: Your guess? "))
            attempts += 1
            
            if guess < secret_number:
                print("📈 Too low! Try higher.")
            elif guess > secret_number:
                print("📉 Too high! Try lower.")
            else:
                print(f"🎉 CONGRATULATIONS! You guessed it in {attempts} attempts!")
                break
                
        except ValueError:
            print("❌ Please enter a valid number!")
    
    else:  # This runs if while loop completes without break
        print(f"💔 Game over! The number was {secret_number}.")

# Start the game
guessing_game()
Nested Loops: Loops Within Loops
Sometimes you need to loop inside another loop - like going through rows and columns!

python
# Multiplication table
print("Multiplication Table (1-5):")
print("    ", end="")
for i in range(1, 6):
    print(f"{i:4}", end="")
print()

for row in range(1, 6):
    print(f"{row}: ", end="")
    for col in range(1, 6):
        product = row * col
        print(f"{product:4}", end="")
    print()  # New line after each row

# Output:
# Multiplication Table (1-5):
#        1   2   3   4   5
# 1:    1   2   3   4   5
# 2:    2   4   6   8  10
# 3:    3   6   9  12  15
# 4:    4   8  12  16  20
# 5:    5  10  15  20  25
Common Loop Patterns You'll Use Every Day
Pattern 1: Processing Lists
python
# Calculate average grade
grades = [85, 92, 78, 90, 88]
total = 0

for grade in grades:
    total += grade

average = total / len(grades)
print(f"📊 Average grade: {average:.1f}")
Pattern 2: Building New Lists
python
# Create list of squares
numbers = [1, 2, 3, 4, 5]
squares = []

for num in numbers:
    squares.append(num ** 2)

print(f"Numbers: {numbers}")
print(f"Squares: {squares}")
Pattern 3: Looping with Index
python
# Loop with index and value
fruits = ["apple", "banana", "cherry"]

for index, fruit in enumerate(fruits):
    print(f"{index + 1}. {fruit}")

# Output:
# 1. apple
# 2. banana
# 3. cherry
Debugging Loops: Common Issues Fixed
Problem 1: Off-by-One Errors
python
# ❌ Wrong (misses last number)
for i in range(1, 5):
    print(i)  # Prints 1,2,3,4 (missing 5)

# ✅ Correct
for i in range(1, 6):
    print(i)  # Prints 1,2,3,4,5
Problem 2: Modifying List While Looping
python
# ❌ Dangerous (can skip elements)
numbers = [1, 2, 3, 4, 5]
for num in numbers:
    if num % 2 == 0:
        numbers.remove(num)  # Bad idea!

# ✅ Safe (create new list or loop backwards)
numbers = [1, 2, 3, 4, 5]
even_numbers = [num for num in numbers if num % 2 == 0]
Your Turn: Practice Exercises
Exercise 1: FizzBuzz
python
# Print numbers 1-100, but:
# - For multiples of 3, print "Fizz"
# - For multiples of 5, print "Buzz"  
# - For multiples of both, print "FizzBuzz"
# - Otherwise, print the number

# Your code here!
Exercise 2: Password Strength Checker
python
# Keep asking for password until it meets:
# - At least 8 characters
# - Contains a number
# - Contains uppercase letter
# Then print "Password accepted!"

# Your code here!
Advanced Loop Techniques (Preview)
List Comprehensions
python
# Instead of:
squares = []
for x in range(10):
    squares.append(x**2)

# You can write:
squares = [x**2 for x in range(10)]