Week 2: Loops + Git Branching

Day 1 For Loops & The range() Function

Learning Objectives: Understand why we use loops. Write for loops with range(). Iterate over strings and lists. Use loop variables effectively.

The range() Function

for i in range(5):       # 0 1 2 3 4
    print(i)
for i in range(2, 7):    # 2 3 4 5 6
    print(i)
for i in range(1, 10, 2):# 1 3 5 7 9
    print(i)
for i in range(10, 0, -1):# 10 9 8 ... 1
    print(i)

Iterating Over Strings & Lists

name = "Python"
for char in name:
    print(char)

fruits = ["apple", "mango", "banana"]
for fruit in fruits:
    print(f"I like {fruit}")

🧑‍💻 Exercise: Sum of First N Numbers

Ask the user for a number n. Calculate and print the sum of all numbers from 1 to n using a for loop.

n = int(input("Enter a number: "))
total = 0
for i in range(1, n + 1):
    total += i
print(f"Sum of 1 to {n} is {total}")

Day 2 While Loops & Indefinite Iteration

Learning Objectives: Understand when to use while vs for. Write condition-based loops. Use sentinel values and counters. Avoid infinite loops.

While Loop Basics

count = 1
while count <= 5:
    print(f"Count: {count}")
    count += 1

Sentinel-Controlled Loop

text = ""
while text != "quit":
    text = input("Enter text (type 'quit' to stop): ")
    if text != "quit":
        print(f"You entered: {text}")
print("Goodbye!")

🧑‍💻 Exercise: Countdown Timer

Ask the user for a starting number and print a countdown from that number to 1, then print "Blast off!" 🚀

start = int(input("Enter countdown start: "))
while start > 0:
    print(start)
    start -= 1
print("🚀 Blast off!")

Day 3 Nested Loops & Patterns

Learning Objectives: Place one loop inside another. Generate multiplication tables. Print star patterns. Understand how inner and outer loops interact.

How Nested Loops Work

for i in range(1, 4):
    for j in range(1, 4):
        print(f"({i}, {j})", end=" ")
    print()

Star Patterns

for i in range(1, 6):
    print("*" * i)   # right triangle
# Inverted:
for i in range(5, 0, -1):
    print("*" * i)

Day 4 Break, Continue & Loop-else

Learning Objectives: Exit loops early with break. Skip iterations with continue. Use the else clause with loops. Combine these with nested loops.

break Example

for num in range(1, 200):
    if num % 7 == 0 and num % 5 == 0:
        print(f"Found: {num}")   # 35
        break

continue Example

for num in range(1, 11):
    if num % 2 == 0:
        continue
    print(num)   # 1 3 5 7 9

Loop-else (Prime Checker)

num = 29
for i in range(2, int(num**0.5)+1):
    if num % i == 0:
        print("Not prime"); break
else:
    print("Prime")

Day 5 Mini-Project: Number Guessing Game

Learning Objectives: Combine loops, conditionals, and user input into a complete game. Use random module. Give feedback. Track attempts.

Project Requirements

1. Generate a random number between 1 and 100.
2. Let the user guess until they get it right.
3. After each guess, say "Too high!" or "Too low!".
4. When correct, print the number of attempts.
5. Bonus: Limit the user to 10 attempts.

import random
secret = random.randint(1, 100)
attempts = 0
while True:
    guess = int(input("Your guess: "))
    attempts += 1
    if guess < secret: print("Too low!")
    elif guess > secret: print("Too high!")
    else: print(f"Correct! {attempts} attempts"); break

Day 6 Git: Branching & Merging

Learning Objectives: Understand why branches are used. Create and switch branches. Merge branches back together. Resolve basic merge conflicts.

Branching Commands

🧑‍💻 Exercise: Create & Merge a Branch

Task: In your python-week1 repo, create a branch called improve-calc. Add modulo and exponent features to calculator.py. Commit, then merge into main.

cd python-week1
git checkout -b improve-calc
# Edit calculator.py ...
git add calculator.py
git commit -m "Added modulo and exponent"
git checkout main
git merge improve-calc -m "Merged improvements"
git branch -d improve-calc

Week 2 Practice Problems

Test your understanding with these problems covering all Week 2 concepts.

🔰 Beginner Level

n = int(input("Enter a number: "))
factorial = 1
for i in range(1, n + 1):
    factorial *= i
print(f"{n}! = {factorial}")

num = int(input("Enter an integer: "))
total = 0
temp = abs(num)
while temp > 0:
    total += temp % 10
    temp //= 10
print(f"Sum of digits = {total}")

n = 5
for i in range(n):
    for j in range(n):
        if i == 0 or i == n-1 or j == 0 or j == n-1:
            print("*", end=" ")
        else:
            print(" ", end=" ")
    print()

⚡ Intermediate Level

n = int(input("How many Fibonacci numbers? "))
a, b = 0, 1
for _ in range(n):
    print(a, end=" ")
    a, b = b, a + b

for num in range(1, 51):
    if num % 3 == 0 and num % 5 == 0:
        print("FizzBuzz")
    elif num % 3 == 0:
        print("Fizz")
    elif num % 5 == 0:
        print("Buzz")
    else:
        print(num)

Unsolved Exercises

Challenge yourself! Try these without peeking at solutions. All concepts are from Week 2.

🔰 Beginner

⚡ Intermediate