`for` loops in Python

# for loops
# About for loops
# for loops are used to iterate over a sequence (list, tuple, string) or other 
# iterable objects.

# Syntax
# for variable in sequence:
#    code block
# Examples

# Iterate over a list
# A list is a collection which is ordered and changeable.
print("\nIterate over a list")
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)
    # Output
    # apple
    # banana
    # cherry

# Iterate over a string
# A string is a sequence of characters
print("\nIterate over a string")
for letter in "apple":
    print(letter)
    # Output
    # a
    # p
    # p
    # l
    # e

# Iterate over a range
# A range is a sequence of numbers, starting from 0 by default, and increments
print("\nIterate over a range")
for i in range(5):
    print(i)
    # Output
    # 0
    # 1
    # 2
    # 3
    # 4
    # Note: The range() function returns a sequence of numbers, starting from 0 
    # by default, and increments by 1 (by default), and stops before a 
    # specified number.

# Iterate over a tuple
# A tuple is a collection which is ordered and unchangeable.
print("\nIterate over a tuple")
colors = ("red", "green", "blue")
for color in colors:
    print(color)
    # Output
    # red
    # green
    # blue

# Iterate over a dictionary
# A dictionary is a collection which is unordered, changeable and indexed.
print("\nIterate over a dictionary")
person = {
    "name": "Alice",
    "age": 25,
    "is_active": True
}
for key in person:
    print(key, person[key])
    # Output
    # name Alice
    # age 25
    # is_active True
    # Note: The for loop iterates over the keys of the dictionary.

# Iterate over a dictionary using items() method
# The items() method returns a view object that displays a list of a given
# dictionary's key-value tuple pair.
print("\nIterate over a dictionary using items() method")
for key, value in person.items():
    print(key, value)
    # Output
    # name Alice
    # age 25
    # is_active True
    # Note: The for loop iterates over the key-value pairs of the dictionary.
    if key == "age" and value >= 18:
        print(person["name"], "is an adult.")

# Iterate over a dictionary using values() method
# The values() method returns a view object that displays a list of all the
# values in the dictionary.
print("\nIterate over a dictionary using values() method")
for value in person.values():
    print(value)
    # Output
    # Alice
    # 25
    # True
    # Note: The for loop iterates over the values of the dictionary.

# Iterate over a dictionary using keys() method
# The keys() method returns a view object that displays a list of all the keys
# in the dictionary.
print("\nIterate over a dictionary using keys() method")
for key in person.keys():
    print(key)
    # Output
    # name
    # age
    # is_active
    # Note: The for loop iterates over the keys of the dictionary.

# Iterate over a dictionary using get() method
# The get() method returns the value of the specified key.
print("\nIterate over a dictionary using get() method")
print(person.get("name"))

# Nested for loops

# clients
clients = [
    {"name": "Alice", "age": 25},
    {"name": "Bob", "age": 30},
    {"name": "Charlie", "age": 35}
]
# products
products = ["apple", "banana", "cherry"]
inventory = {
    "apple": 10,
    "banana": 20,
    "cherry": 30
}
# orders
orders = [
    {"client": "Alice", "product": "apple"},
    {"client": "Bob", "product": "banana"},
    {"client": "Charlie", "product": "cherry"}
]

# Iterate over clients
print("\nIterate over clients")
for client in clients:
    print(client["name"], client["age"])
    # Output
    # Alice 25
    # Bob 30
    # Charlie 35

# Iterate over products
print("\nIterate over products")
for product in products:
    print(product)
    # Output
    # apple
    # banana
    # cherry

# Iterate over orders
print("\nIterate over orders")
for order in orders:
    print(order["client"], order["product"])
    # Output
    # Alice apple
    # Bob banana
    # Charlie cherry

# Iterate over orders and products and update inventory
print("\nIterate over orders and products and update inventory")
for order in orders:
    for product in products:
        if order["product"] == product:
            inventory[product] -= 1
            print(order["client"], "ordered", order["product"])
            print("Inventory of", product, "is", inventory[product])
            # Output
            # Alice ordered apple
            # Inventory of apple is 9
            # Bob ordered banana
            # Inventory of banana is 19
            # Charlie ordered cherry
            # Inventory of cherry is 29
# Note: The nested for loop iterates over the orders and products and updates
# the inventory of the products.