01_for_loop.py

"""
================================================================================
File: 01_for_loop.py
Topic: For Loops in Python
================================================================================

This file demonstrates the 'for' loop in Python, which is used to iterate
over sequences (lists, tuples, strings, ranges, etc.) or any iterable object.

Key Concepts:
- Basic for loop syntax
- range() function for numeric iterations
- Iterating over different data types
- enumerate() for index and value
- zip() for parallel iteration
- Nested for loops

================================================================================
"""

# -----------------------------------------------------------------------------
# 1. Basic For Loop
# -----------------------------------------------------------------------------
# Iterate over items in a sequence

print("--- Basic For Loop ---")

fruits = ["apple", "banana", "cherry", "date"]

for fruit in fruits:
    print(f"I like {fruit}")

# -----------------------------------------------------------------------------
# 2. Using range() Function
# -----------------------------------------------------------------------------
# range(start, stop, step) - generates numbers from start to stop-1

print("\n--- Using range() ---")

# range(5) generates 0, 1, 2, 3, 4
print("range(5):")
for i in range(5):
    print(i, end=" ")
print()

# range(2, 8) generates 2, 3, 4, 5, 6, 7
print("\nrange(2, 8):")
for i in range(2, 8):
    print(i, end=" ")
print()

# range(0, 10, 2) generates 0, 2, 4, 6, 8 (step of 2)
print("\nrange(0, 10, 2):")
for i in range(0, 10, 2):
    print(i, end=" ")
print()

# Counting backwards: range(10, 0, -1)
print("\nrange(10, 0, -1) - Countdown:")
for i in range(10, 0, -1):
    print(i, end=" ")
print("Blastoff!")

# -----------------------------------------------------------------------------
# 3. Iterating Over Strings
# -----------------------------------------------------------------------------
# Each character in a string is an item

print("\n--- Iterating Over Strings ---")

word = "Python"
print(f"Characters in '{word}':")

for char in word:
    print(f"  {char}")

# -----------------------------------------------------------------------------
# 4. Using enumerate() - Get Index and Value
# -----------------------------------------------------------------------------
# enumerate() provides both the index and the item

print("\n--- Using enumerate() ---")

languages = ["Python", "JavaScript", "C++", "Rust"]

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

# Start from a custom number
print("\nWith custom start:")
for rank, language in enumerate(languages, start=1):
    print(f"Rank {rank}: {language}")

# -----------------------------------------------------------------------------
# 5. Using zip() - Parallel Iteration
# -----------------------------------------------------------------------------
# zip() combines multiple iterables and iterates over them together

print("\n--- Using zip() ---")

names = ["Alice", "Bob", "Charlie"]
ages = [25, 30, 35]
cities = ["New York", "London", "Tokyo"]

# Iterate over multiple lists simultaneously
for name, age, city in zip(names, ages, cities):
    print(f"{name} is {age} years old and lives in {city}")

# -----------------------------------------------------------------------------
# 6. Iterating Over Dictionaries
# -----------------------------------------------------------------------------
# Different ways to loop through dictionary data

print("\n--- Iterating Over Dictionaries ---")

person = {
    "name": "Baraa",
    "age": 25,
    "city": "Gaza",
    "profession": "Developer"
}

# Keys only (default)
print("Keys:")
for key in person:
    print(f"  {key}")

# Values only
print("\nValues:")
for value in person.values():
    print(f"  {value}")

# Both keys and values
print("\nKey-Value pairs:")
for key, value in person.items():
    print(f"  {key}: {value}")

# -----------------------------------------------------------------------------
# 7. Nested For Loops
# -----------------------------------------------------------------------------
# A loop inside another loop

print("\n--- Nested For Loops ---")

# Multiplication table
print("Multiplication Table (1-5):")
for i in range(1, 6):
    for j in range(1, 6):
        print(f"{i * j:3}", end=" ")
    print()  # New line after each row

# Working with 2D lists (matrices)
print("\n2D Matrix:")
matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

for row in matrix:
    for cell in row:
        print(f"{cell}", end=" ")
    print()

# -----------------------------------------------------------------------------
# 8. Else Clause in For Loop
# -----------------------------------------------------------------------------
# The else block executes when the loop completes without break

print("\n--- For-Else Clause ---")

# Search for a number
numbers = [1, 3, 5, 7, 9]
search_for = 5

for num in numbers:
    if num == search_for:
        print(f"Found {search_for}!")
        break
else:
    print(f"{search_for} was not found.")

# -----------------------------------------------------------------------------
# 9. List Comprehension (Related to For Loops)
# -----------------------------------------------------------------------------
# A concise way to create lists using for loops

print("\n--- List Comprehension Preview ---")

# Traditional way
squares_traditional = []
for x in range(1, 6):
    squares_traditional.append(x ** 2)
print(f"Traditional: {squares_traditional}")

# List comprehension way
squares_comprehension = [x ** 2 for x in range(1, 6)]
print(f"Comprehension: {squares_comprehension}")

# -----------------------------------------------------------------------------
# 10. Practical Examples
# -----------------------------------------------------------------------------

print("\n--- Practical Examples ---")

# Sum of numbers
numbers = [10, 20, 30, 40, 50]
total = 0
for num in numbers:
    total += num
print(f"Sum of {numbers} = {total}")

# Finding maximum
values = [23, 45, 12, 78, 34]
maximum = values[0]
for value in values:
    if value > maximum:
        maximum = value
print(f"Maximum in {values} = {maximum}")

# Counting vowels in a string
text = "Hello, World!"
vowels = "aeiouAEIOU"
vowel_count = 0
for char in text:
    if char in vowels:
        vowel_count += 1
print(f"Vowels in '{text}': {vowel_count}")