Python Loops and Iteration

Topic: Loops and Iteration

Mastering the power of repetition and automation.

1. The Concept of Iteration

In programming, Iteration simply means repeating a process. Instead of writing the same line of code 100 times, we use a loop. Python provides two main types of loops: the For Loop and the While Loop.

2. The "For" Loop (Fixed Repeats)

Use a for loop when you know exactly how many times the code should run. It is often paired with the range() function.

# range(start, stop)
for i in range(1, 6):
    print("Attempt number:", i)

Pro Tip: range(1, 6) starts at 1 and stops at 5. It never includes the final "stop" number!

3. The "While" Loop (Condition Based)

A while loop keeps running as long as a condition is True. It is perfect for situations where you don't know when the loop will end.

count = 5
while count > 0:
    print("Countdown:", count)
    count = count - 1
print("Blast off! 🚀")

⚠️ The Infinite Loop: If you forget to update your variable (like count - 1), the loop will never stop. This can crash your program!

4. Deep Dive: Six Real-World Examples

To master loops, you must understand how they apply to different scenarios. Here are three examples for each type:

A. For Loop Scenarios (The Accountant)

1. Class Attendance

Processing a list of names one by one.

students = ["Joseph", "Blessing"]
for name in students:
  print(name, "is present.")

2. Backward Timer

Using range to count down with a step of -1.

for sec in range(10, 0, -1):
  print("Seconds left:", sec)

3. Email Scanner

Looping through characters in a string.

email = "admin@cmp.com"
for char in email:
  if char == "@":
    print("Found the @ symbol!")

B. While Loop Scenarios (The Security Guard)

1. Game Health Bar

Loop runs as long as the player is alive.

hp = 100
while hp > 0:
  hp -= 20
  print("Remaining HP:", hp)

2. Infinite Input

Running until the user decides to 'quit'.

msg = ""
while msg != "quit":
  msg = input("Say something: ")

3. Savings Goal

Looping until a financial target is met.

saved = 0
while saved < 500:
  saved += int(input("Add cash: "))

5. Additional Loop Control: The 'Continue'

While break stops the loop completely, continue skips just one iteration and moves to the next cycle.

for n in range(1, 6):
    if n == 3:
        continue
    print(n)

6. Nested Loops (Loops inside Loops)

A nested loop is useful for working with tables, patterns, and combinations.

for i in range(1, 4):
    for j in range(1, 3):
        print("i =", i, "j =", j)

💻 Practical Coding Lab

Challenge: The Multiplication Table

Write a program that asks for a number and prints its multiplication table from 1 to 12.

Click to view Solution Code

num = int(input("Show table for: "))
for i in range(1, 13):
    ans = num * i
    print(num, "x", i, "=", ans)

📝 Topic 3 Quiz

1. Which loop is best when you don't know how many times to repeat?
A) For loop
B) While loop

2. What command is used to exit a loop immediately?
A) continue
B) break

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