No Fluff Guide to Python - P12

"History is about loops and continuum."

while true:
    dispense(coldDrink_Can)

Imagine you have a big box of toys:

you want to go through each toy and play with it
but instead of picking up each toy one by one, you want a way to play with all the toys without lifting them individually

that's where loops in Python come in handy
a loop is like a magical robot arm that helps you go through each toy in the box automatically

it saves you time and effort.

In Python:

you can use a loop to repeat a set of instructions
over and over again
until a certain condition is met
Example

you can tell the loop to play with each toy in the box
until there are no more toys left

example:

toys = ["car", "ball", "doll", "blocks"]

for toy in toys:
    play_with(toy)

The for loop goes through each toy (toy) in the toys list
it tells our magical robot arm to play_with() each toy
It will keep playing with each toy

until it has gone through all the toys in the box

A real-world application:

Have you ever seen a vending machine, like the ones that dispense snacks or drinks?
Vending machines use loops to give you options and repeat the process until you make a selection.
Here's a simplified explanation of how a vending machine might work:

You approach the vending machine and see a list of snacks.
The vending machine has a loop that shows each snack option, one after the other.
You can make a choice by pressing a button corresponding to the snack you want.
The loop keeps running until you make a selection or decide not to buy anything.

Python3:

we have three types of loops:

the for loop,
the while loop, and
the do-while loop (which is not directly available in Python but can be achieved using a while loop)

We usually use Loops to:

Execute a code over and over
iterate over a list, dictionary, set, etc.

Another scenario:

you want to calculate the sum of all numbers
from 1 to 100
we can do this using a for loop

total_sum = 0

for num in range(1, 101):
    total_sum += num

print(total_sum)

We use the range() function to generate a sequence of numbers from 1 to 100.

The loop iterates over each number and adds it to the total_sum variable.

Another example:

you want to find the factorial of a given number
lets try this using a while loop

num = 6
factorial = 1

while num > 1:
    factorial *= num
    num -= 1

print(factorial)

The loop multiplies the factorial variable by num and reduces num by 1 in each iteration until num becomes 1.

The key difference between for and while loops

the for loop is used when you know the number of iterations in advance
the while loop is used when the number of iterations depends on a condition.

Let's explore some real-world examples of loops and their connection with data structures.

While Loop and Dictionary:

Let's consider a scenario
you have a dictionary representing the inventory of a store
you want to check the stock levels of each item
until you find an item that is out of stock.

Here's an example code:

inventory = {
    "apple": 10,
    "banana": 5,
    "cherry": 0,
    "date": 3,
    "elderberry": 8
}

item = input("Enter an item name: ")

while item in inventory:
    if inventory[item] == 0:
        print(item + " is out of stock.")
        break
    else:
        print(item + " is in stock.")
        item = input("Enter another item name: ")

In this example:

the while loop checks if the entered item

exists in the inventory dictionary.

If the item is in stock (quantity greater than 0), it informs the user.
If the item is out of stock (quantity equals 0), it breaks out of the loop.

While Loop and Tuple:

A real-world IT-related scenario:

tuple containing employee records

Name, Designation

generate a report to display names with profession.

# Tuple representing a list of IT employees
it_employees = (
    ("John Doe", "Software Engineer"),
    ("Jane Smith", "Network Administrator"),
    ("Mike Johnson", "Database Administrator"),
    ("Sarah Williams", "System Analyst")
)

# Iterating over the tuple using a for loop
for employee in it_employees:
    name, job_title = employee
    print(f"{name} works as a {job_title}.")

# Output:
# John Doe works as a Software Engineer.
# Jane Smith works as a Network Administrator.
# Mike Johnson works as a Database Administrator.
# Sarah Williams works as a System Analyst.

In this example:

we have a tuple called it_employees that represents a list of IT employees.
Each employee is a tuple consisting of their name and job title.
The code uses a for loop to iterate over the it_employees tuple.
Inside the loop, we unpack each employee tuple into name and job_title variables.
Then, it prints out the name and job title of each employee.

While Loop and List of Lists:

A real-world Instagram app related scenario:

user posts are stored in a variable
loop through all posts

print info about that post

instagram_posts = [
    ["User1", "Caption1", 100, ["#nature", "#photography"]],
    ["User2", "Caption2", 200, ["#sunset", "#beach"]],
    ["User3", "Caption3", 150, ["#food", "#yum"]],
    ["User4", "Caption4", 300, ["#fashion", "#ootd"]]
]

for post in instagram_posts:
    username = post[0]
    caption = post[1]
    likes = post[2]
    hashtags = post[3]

    print(f"Username: {username}")
    print(f"Caption: {caption}")
    print(f"Likes: {likes}")
    print("Hashtags:")
    for tag in hashtags:
        print(tag)
    print("-" * 20)

In this example:

we have a list called instagram_posts

where each element is a list representing an Instagram post

each post contains

username,
caption,
number of likes, and
a list of hashtags

the code iterates over each post in the instagram_posts list and

extracts the relevant information: username, caption, likes, and hashtags.
then prints out this information, including each hashtag on a separate line.
A line of dashes is printed after each post for visual separation.

While Loop and Sets:

A real-world IT-related scenario:

technologies = {"Python", "Java", "JavaScript", "C#", "Ruby", "Go"}

print("List of Technologies:")
for tech in technologies:
    print(tech)

In this example:

we have a set called technologies that represents

a collection of IT technologies.
Each technology name is a separate element in the set.

The code iterates over the set using a for loop and
assigns each technology to the variable tech in each iteration.
It then prints out the name of each technology in the set.

WhatsApp and Python

Scenario:

let's assume you have a list of chat messages stored in Python
you want to display a limited number of messages at a time
to simulate the loading of more messages when requested

we can use a loop along with user input.

chat_messages = [
    "Hey, how are you?",
    "I'm good, thanks! How about you?",
    "I'm doing great. What have you been up to?",
    "Just working on a coding project. How about you?",
    "I've been studying for exams. It's been hectic!",
    "I can imagine. Good luck with your exams!",
    "Thanks! So, what's new with you?"
    # More chat messages...
]

the chat_messages list represents the collection of chat messages

We define some predefined variables:

messages_per_page

how many messages are loaded initially

total_messages

total number of messages in the chat

current_page

current page number

messages_per_page = 3  # Number of messages to display per page
total_messages = len(chat_messages)
current_page = 1

The display_messages() function is used to print a specified range of messages.

We initially display the first set of messages using this function.

def display_messages(start_index, end_index):
    for i in range(start_index, end_index):
        print(chat_messages[i])

# Display the initial set of messages
display_messages(0, messages_per_page)

load_more_messages( ):

function is responsible for calculating
the start and end indices of the next set of messages.
It checks if there are more messages to display and
calls the display_messages() function accordingly.

def load_more_messages():
    global current_page

    start_index = current_page * messages_per_page
    end_index = (current_page + 1) * messages_per_page

    # Check if there are more messages to display
    if start_index < total_messages:
        display_messages(start_index, end_index)
        current_page += 1
    else:
        print("No more messages to display.")

The loop continuously asks the user if they want to load more messages. If the user chooses to load more, the load_more_messages() function is called. If the user chooses not to load more, the loop breaks, and the chat ends.

# Ask the user if they want to load more messages
while True:
    choice = input("Do you want to load more messages? (y/n): ")

    if choice.lower() == "y":
        load_more_messages()
    elif choice.lower() == "n":
        break
    else:
        print("Invalid choice. Please enter 'y' or 'n'.")

print("End of chat.")

Cryptography and Python:

A digital wallet recovery code:

also known as a wallet recovery seed or mnemonic phrase
is used as a backup and recovery mechanism for cryptocurrency wallets,
particularly software wallets or hardware wallets.
This recovery code is a series of words

usually 12, 24, or 25 words

that serves as a master key
to access and recover your cryptocurrency funds

in case of loss, theft, or damage to the wallet itself.

The recovery code is a critical component of cryptocurrency wallet security.
It ensures that even if you lose your wallet or it gets stolen

you can regain access to your digital assets.

However, it's equally important to safeguard the recovery code diligently,
as anyone who gains access to it can potentially steal your cryptocurrency holdings.

Suppose that we’re writing a digital wallet in python and one of our tasks is to write a code that:

Accepts 5 words as recovery words
Store the words into a List
Displays the List

Let's start by writing the Python code without using loops:

# Accepting 5 words as recovery words
word1 = input("Enter word 1: ")
word2 = input("Enter word 2: ")
word3 = input("Enter word 3: ")
word4 = input("Enter word 4: ")
word5 = input("Enter word 5: ")

# Storing the words into a List
recovery_words = [word1, word2, word3, word4, word5]

# Displaying the List
print(recovery_words)

Now, let's write the Python code using loops to improve the code's efficiency and reduce redundancy:

# Initializing an empty list
recovery_words = []

# Accepting 5 words as recovery words using a loop
for i in range(5):
    word = input("Enter word {}: ".format(i+1))
    recovery_words.append(word)

# Displaying the List
print(recovery_words)

Good Luck!

Until next time.. Keep practicing.

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