# Iterate over a list
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)
# apple
# banana
# cherry

# Iterate over a string
for char in "Python":
    print(char, end=" ")
# P y t h o n

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

# range(start, stop) - start to stop-1
for i in range(2, 7):
    print(i, end=" ")
# 2 3 4 5 6

# range(start, stop, step)
for i in range(0, 20, 3):
    print(i, end=" ")
# 0 3 6 9 12 15 18

# Counting backwards
for i in range(10, 0, -1):
    print(i, end=" ")
# 10 9 8 7 6 5 4 3 2 1

# Even numbers
for i in range(0, 11, 2):
    print(i, end=" ")
# 0 2 4 6 8 10

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

for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")
# 0: apple
# 1: banana
# 2: cherry
# 3: date

# Custom starting index
for i, fruit in enumerate(fruits, start=1):
    print(f"{i}. {fruit}")
# 1. apple
# 2. banana
# 3. cherry
# 4. date

student = {"name": "Alice", "age": 25, "grade": "A"}

# Iterate over keys (default)
for key in student:
    print(key)
# name, age, grade

# Iterate over values
for value in student.values():
    print(value)
# Alice, 25, A

# Iterate over key-value pairs
for key, value in student.items():
    print(f"{key}: {value}")
# name: Alice
# age: 25
# grade: A

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

for name, age, city in zip(names, ages, cities):
    print(f"{name} ({age}) from {city}")
# Alice (25) from New York
# Bob (30) from London
# Charlie (35) from Tokyo

# Create a dictionary from two lists
keys = ["name", "age", "city"]
values = ["Alice", 25, "NYC"]
result = dict(zip(keys, values))
print(result)  # {'name': 'Alice', 'age': 25, 'city': 'NYC'}

# zip stops at shortest sequence
a = [1, 2, 3, 4, 5]
b = ["a", "b", "c"]
for x, y in zip(a, b):
    print(x, y)
# 1 a, 2 b, 3 c

# Find the first negative number
numbers = [3, 7, -1, 9, -5, 2]

for num in numbers:
    if num < 0:
        print(f"Found negative: {num}")
        break
    print(f"Checking: {num}")
# Checking: 3
# Checking: 7
# Found negative: -1

# Print only even numbers
for i in range(10):
    if i % 2 != 0:
        continue
    print(i, end=" ")
# 0 2 4 6 8

# Placeholder for future code
for i in range(5):
    if i == 3:
        pass  # TODO: handle special case
    print(i)

# Search for a value
numbers = [1, 3, 5, 7, 9]
target = 4

for num in numbers:
    if num == target:
        print(f"Found {target}!")
        break
else:
    print(f"{target} not found in the list")
# 4 not found in the list

# Example: check if number is prime
def is_prime(n):
    if n < 2:
        return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % 2 == 0:
            return False
    else:
        return True

print(is_prime(17))  # True
print(is_prime(15))  # False

# Multiplication table
for i in range(1, 6):
    for j in range(1, 6):
        print(f"{i*j:4}", end="")
    print()

#    1   2   3   4   5
#    2   4   6   8  10
#    3   6   9  12  15
#    4   8  12  16  20
#    5  10  15  20  25

# Pattern: right triangle
rows = 5
for i in range(1, rows + 1):
    print("* " * i)
# *
# * *
# * * *
# * * * *
# * * * * *

# Flatten nested list
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
flat = []
for row in matrix:
    for num in row:
        flat.append(num)
print(flat)  # [1, 2, 3, 4, 5, 6, 7, 8, 9]

# List of tuples
students = [
    ("Alice", 90),
    ("Bob", 85),
    ("Charlie", 92)
]

for name, score in students:
    print(f"{name}: {score}")

# With enumerate
for i, (name, score) in enumerate(students, 1):
    print(f"{i}. {name} scored {score}")

# Nested dictionaries
school = {
    "math": {"teacher": "Dr. Smith", "students": 30},
    "science": {"teacher": "Dr. Jones", "students": 25}
}

for subject, details in school.items():
    print(f"{subject}: {details['teacher']} ({details['students']} students)")

# Use range(len()) only when you need the index
# AVOID:
for i in range(len(fruits)):
    print(fruits[i])

# PREFER:
for fruit in fruits:
    print(fruit)

# If you need index, use enumerate:
for i, fruit in enumerate(fruits):
    print(i, fruit)

# Avoid modifying a list while iterating over it
# WRONG:
numbers = [1, 2, 3, 4, 5]
# for num in numbers:
#     if num % 2 == 0:
#         numbers.remove(num)  # Dangerous!

# CORRECT: iterate over a copy or use list comprehension
numbers = [num for num in numbers if num % 2 != 0]
print(numbers)  # [1, 3, 5]

"""
Count word frequency in a text.
"""

text = """
Python is great. Python is popular.
Python is used for web development and data science.
Many developers love Python.
"""

# Clean and split
words = text.lower().split()

# Count frequencies
frequency = {}
for word in words:
    # Remove punctuation
    word = word.strip(".,!?")
    frequency[word] = frequency.get(word, 0) + 1

# Sort by frequency (descending)
sorted_words = sorted(frequency.items(), key=lambda x: x[1], reverse=True)

print("Word Frequency:")
print("-" * 25)
for word, count in sorted_words:
    bar = "█" * count
    print(f"{word:<15} {count:>2} {bar}")