🧠 LEGB Rule in Python (Scope Resolution)

When Python looks for a variable, 
it follows a fixed order called LEGB.

L → Local 
E → Enclosing 
G → Global 
B → Built-in 

Python searches in this order.


1️⃣ Local Scope (L) 📍 
Variables defined inside a function.

x = 10

def func():
    x = 5
    print(x)

func()

Output:
5
➤ Python finds x inside the function first.


2️⃣ Enclosing Scope (E) 🔄 
Variables in outer function (nested functions).

def outer():
    x = 20
    def inner():
        print(x)
    inner()

outer()

Output:
20
➤ Python finds x in the enclosing function.


3️⃣ Global Scope (G) 🌍 
Variables defined outside all functions.

x = 30

def func():
    print(x)

func()

Output:
30
➤ Python uses global x.


4️⃣ Built-in Scope (B) ⚙️ 
Predefined names like len, print, etc.

print(len([1, 2, 3]))

Output:
3

💡 Search Order

Local → Enclosing → Global → Built-in 

Python stops searching once it finds the name.

🚀 List vs Tuple in Python

Both store collections of data. 
But they differ in mutability and internal behavior.

1️⃣ List (Mutable) 📦

Can be modified after creation.

nums = [1, 2, 3]
nums.append(4)
print(nums)

Output:
[1, 2, 3, 4]
➤ How: Stored as a dynamic array 
➤ Wins: Flexible, easy to modify 
➤ Risk: Slightly higher memory usage 

2️⃣ Tuple (Immutable) 🔒

Cannot be modified after creation.

nums = (1, 2, 3)
nums.append(4)

Output:
AttributeError: 'tuple' object has no attribute 'append'
➤ How: Fixed-size structure 
➤ Wins: Faster iteration, lower memory usage 
➤ Risk: No modification allowed 

💡 Key Difference

• List → Mutable & flexible 
• Tuple → Immutable & lightweight 

Use List when data changes. 
Use Tuple when data should stay constant.

NumPy Cheatsheet (Basic to Advanced)

🐍 Let’s Fix How You’re Learning Python

If you feel slow in Python, it usually is not because Python is hard. It is because of the learning approach.

Let me be direct.

⚠️ Avoid these habits

- Jumping between many tutorials
- Copying code without thinking
- Ignoring error messages
- Watching more than building

👉 Instead, build this discipline

- Follow one main learning path
- After every concept, write your own small code
- When an error appears, read it slowly
- Build small projects every week

📌 Python becomes easier the moment you start treating it like a tool, not a subject.

Keywords in Python

🧠 Learn to Trace Code by Hand

Before running code, pause and predict the output. This builds real understanding.

Consider this:

x = 0

for i in range(3):
    x += i

print(x) 

Walk through slowly.

1. Start: x = 0

2. i = 0 → x = 0

3. i = 1 → x = 1

4. i = 2 → x = 3

Final output:

3

This habit strengthens your debugging ability more than passive reading ever will.

Try this daily with small snippets.

Python Basics Cheat Sheet (Beginner Friendly)

🐍 Python Functions (def) ⚙️

Functions help organize code into reusable blocks, making programs cleaner and more efficient. Essential for writing modular and scalable code.

👉 They are very important for avoiding repetitive code and building complex applications.

🔹 1. What is a Function?

A function is a block of code that only runs when it is called. You can pass data, known as parameters, into a function.

Example:

def greet():
    print("Hello from a function!")

🔹 2. Defining & Calling a Function

We use the def keyword to define a function, then call it by its name.

Syntax:

def function_name(parameters):
    # code to execute
function_name(arguments) # call the function

Example:

def say_hello():
    print("Hello, Python learner!")

say_hello() # calling the function

Output: Hello, Python learner!

🔹 3. Functions with Parameters & Arguments

Parameters are variables listed inside the parentheses in the function definition. Arguments are the actual values sent when calling the function.

Example:

def welcome_user(name): # 'name' is a parameter
    print(f"Welcome, {name}!")

welcome_user("Alice") # "Alice" is an argument
welcome_user("Bob")

Output:
Welcome, Alice!
Welcome, Bob!

🔹 4. Return Values

Functions can return data as a result using the return keyword.

Example:

def add_numbers(a, b):
    return a + b

result = add_numbers(5, 7)
print(result)

Output: 12

🔹 5. Common Function Uses

• Calculations: Performing mathematical operations.
• Data Processing: Transforming inputs.
• User Interaction: Handling prompts and responses.
• Code Reusability: Doing the same task many times.

🎯 Today's Goal

✔️ Understand what functions are
✔️ Define and call functions
✔️ Use parameters and arguments
✔️ Return values from functions

👉 Functions are fundamental building blocks in almost every Python project.

Learn Python

This is Scrimba's official Python course featuring their unique interactive scrim format. It offers 58 interactive video lessons where you can pause the screencast and edit the instructor's code directly in your browser with no local setup required. Its great for hands-on learners who want to code actively during the lesson rather than passively watching. No prerequisites are required.

📚 58 interactive lessons covering Python fundamentals: variables, data types, strings, lists, dictionaries, loops, functions, and file handling—all with built-in coding challenges

⏰ Duration: 5.6 hours

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🔗 Course Link


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🐍Python Lists (Data Structures) 📦

🔹 1. What is a List?

A list is a sequence of values (items). They are ordered, changeable (mutable), and allow duplicate members. Defined by square brackets [].

Example:

my_list = ["apple", 3.14, True, 100]
print(my_list)

Output: ['apple', 3.14, True, 100]

🔹 2. Accessing List Items

Items are accessed by their index, which starts at 0 for the first item.

Example:

fruits = ["apple", "banana", "cherry"]
print(fruits[0]) # First item
print(fruits[2]) # Third item
print(fruits[-1]) # Last item

Output:
apple
cherry
cherry

🔹 3. Modifying List Items

You can change an item by referring to its index.

Example:

colors = ["red", "green", "blue"]
colors[1] = "yellow" # Change 'green' to 'yellow'
print(colors)

Output: ['red', 'yellow', 'blue']

🔹 4. Adding Items to a List

• .append(): Adds an item to the end of the list.
• .insert(index, item): Adds an item at a specific index.

Example:

names = ["Alice", "Bob"]
names.append("Charlie") # Add to end
names.insert(0, "David") # Add at the beginning
print(names)

Output: ['David', 'Alice', 'Bob', 'Charlie']

🔹 5. Removing Items from a List

• .remove(item): Removes the first occurrence of a specified item.
• .pop(index): Removes (and returns) the item at a specified index (or the last item if no index is given).
• del list[index]: Deletes the item at a specific index.

Example:

numbers = [10, 20, 30, 20, 40]
numbers.remove(20) # Removes first '20'
del numbers[0]     # Removes '10'
print(numbers)

Output: [30, 20, 40]

🎯 Today's Goal(What you should do)

✔️ Understand what lists are and how to create them
✔️ Access items using indexing
✔️ Modify, add, and remove items from lists

🐍 Python For Loops (Iteration) 🔄

For loops are used to iterate over a sequence (like a list, tuple, string, or range) or other iterable objects. They let you execute a block of code repeatedly for each item.

👉 They are essential for automating tasks and processing collections of data efficiently.

🔹 1. What is a For Loop?

A for loop executes a set of statements, once for each item in a collection.

Example:

for character in "Python":
    print(character)

Output:
P
y
t
h
o
n

🔹 2. Looping Through a List

This is one of the most common uses: going through each item in a list.

Syntax:

for item in list_name:
    # code to execute for each item

Example:

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

Output:
I like apple.
I like banana.
I like cherry.

🔹 3. The range() Function

The range() function generates a sequence of numbers, often used to loop a specific number of times.

• range(stop): Numbers from 0 up to (but not including) stop.
• range(start, stop): Numbers from start up to (not including) stop.
• range(start, stop, step): Numbers from start up to stop, increasing by step.

Example:

for i in range(3): # Loop 3 times (0, 1, 2)
    print(f"Iteration {i}")

Output:
Iteration 0
Iteration 1
Iteration 2

🔹 4. break and continue Statements

• break: Stops the loop completely, even if the iterable hasn't finished.
• continue: Skips the rest of the current iteration and moves to the next.

Example (break):

for number in range(1, 6):
    if number == 4:
        break # Stop when number is 4
    print(number)

Output:
1
2
3

Example (continue):

for item in ["A", "B", "C", "D"]:
    if item == "C":
        continue # Skip 'C'
    print(item)

Output:
A
B
D

🎯 Today's Goal(What you should do)

✔️ Understand what for loops are
✔️ Iterate over lists, strings, and ranges (using your Python editor)
✔️ Use break and continue to control loop flow (using your Python editor)

🐍 Python If-Else Statements (Conditionals) 🤔

If-Else statements allow your program to make decisions and execute different code blocks based on conditions. They are fundamental for creating dynamic and responsive applications.

👉 Essential for controlling the flow of your program.

🔹 1. What are Conditional Statements?

They test a condition. If the condition is True, one block of code runs. If False, another block (or nothing) might run.

Example:

temperature = 25
if temperature > 20:
    print("It's warm!")

Output: It's warm!

🔹 2. The if Statement

The simplest conditional, executing code only when a condition is True.

Syntax:

if condition:
    # code to run if condition is True

Example:

age = 18
if age >= 18:
    print("You are an adult.")

Output: You are an adult.

🔹 3. The else Statement

Executes a block of code when the if condition is False.

Syntax:

if condition:
    # code if True
else:
    # code if False

Example:

score = 75
if score >= 90:
    print("Excellent!")
else:
    print("Good effort!")

Output: Good effort!

🔹 4. The elif (Else If) Statement

Allows you to check multiple conditions sequentially. If the first if is False, it checks elif, and so on.

Syntax:

if condition1:
    # code if condition1 is True
elif condition2:
    # code if condition2 is True
else:
    # code if all conditions are False

Example:

time = 14
if time < 12:
    print("Good morning!")
elif time < 18:
    print("Good afternoon!")
else:
    print("Good evening!")

Output: Good afternoon!

🔹 5. Short Hand If / Ternary Operator

A concise way to write simple if-else statements on a single line.

Example:

a = 10
b = 5
print("A is greater") if a > b else print("B is greater")

Output: A is greater

🎯 Today's Goal(What you should do)

✔️ Understand how to use if, elif, and else
✔️ Make your programs respond to different inputs
✔️ Use shorthand for simple conditions

👉 Conditional statements are the backbone of any interactive and logical Python program. It's crucial you understand them well.