Python Loops 🔁

Automation & Repetition

Session 3: For & While Loops

What Are Loops? 🤔

Loops make computers repeat code. Without loops, you'd write the same code over and over. Computers are powerful because they never get tired!

Why Loops Matter:

AI trains by repeating millions of times
Servers process thousands of requests in loops
Games run loops to update graphics 60 times per second
Automation means doing the same task repeatedly

For Loops: Counting 📊

A for loop repeats code a specific number of times. Perfect when you know exactly how many repetitions you need.

Code Example - Print Numbers 1-5:

for i in range(1, 6):
  print(i)

Output: 1, 2, 3, 4, 5

range(1, 6) means start at 1, go up to (but not including) 6

For Loop: Multiplication Table 🔢

Create a 7 Times Table:

for i in range(1, 11):
  answer = 7 * i
  print(f"7 ×
                    {i} = {answer}")

Output:
7 × 1 = 7
7 × 2 = 14
... (continues to 7 × 10 = 70)

While Loops: Unknown Repetitions ⏰

A while loop repeats while a condition is true. Perfect when you don't know how many repetitions you need.

Countdown Example:

count = 10
while count > 0:
  print(count)
  count
                    = count - 1
print("Blastoff!")

Output: 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, Blastoff!

While Loop: User Input 💬

A common use: repeat until user says to stop.

Code Example:

answer = ""
while answer != "quit":
  answer = input("Say
                    something (or 'quit'): ")
  if answer != "quit":
    print("You
                    said: " + answer)

Loop continues until user types "quit"

For vs While: Which to Use? 🤷

Use For Loop When:

You know exactly how many times to repeat
You need to count through numbers
Iterating through lists (next topic!)

Use While Loop When:

You don't know how many repetitions
Condition-based repetition
Waiting for user input

Project: Guessing Game 🎮

Code:

import random
secret = random.randint(1, 10)
guess = 0
while guess !=
                    secret:
  guess = int(input("Guess 1-10: "))
  if guess ==
                    secret:
    print("Correct!")
  elif guess < secret:

                            print("Too
                        low!")
  else:
    print("Too high!")

Break & Continue 🛑

Control loop flow with special keywords:

Break - Exit Loop Immediately:

while True:
  answer = input("Want to continue?
                    ")
  if answer == "no":
    break # Exit loop
print("Done!")
                

Continue - Skip Rest of Loop:

for i in range(1, 6):
  if i ==
                    3:
    continue # Skip 3
  print(i) # Prints 1, 2, 4, 5

Nested Loops 🔁🔁

Loops inside loops! Useful for creating patterns.

Times Table Grid:

for i in range(1, 4):
  for j in range(1,
                    4):
    result = i * j
    print(f"{result}", end="
                    ")
  print() # New line

Output: A 3×3 multiplication table

Common Loop Mistakes ❌

Watch Out For:

Infinite loops: while True without a break (program hangs)
Off-by-one errors: range(5) gives 0-4, not 1-5
Forgetting indentation: Code inside loop must be indented
Updating wrong variable: In while, update the condition variable!

What We Learned 🎓

For loops repeat a known number of times
While loops repeat while a condition is true
range() generates sequences of numbers
break exits a loop immediately
continue skips to next iteration
Nested loops create complex patterns
Loops are essential for automation!

Automation Mastered! 🎉

Your programs can now do repetitive tasks

Next Chapter: How AI Actually Works!