🌟 Session 1 of 12
Session 1

Introduction to Python

Your programming journey starts here! Learn what Python is and write your first code.

🎯 What You'll Learn

🐍

What is Python?

The language that powers AI, web, and more

📦

Variables

Store and retrieve data easily

📝

Naming Rules

7 rules for valid variable names

🖨️

print() & id()

Display output and check memory

📘 Same topic in the course notebook

Session_1 in the course source has Introduction_to_Python and Variables in Python notebooks: same ideas (what is Python, variables, naming, print, id). Run those cells to practice.

🐍 What is Python?

The Robot Butler Story

Imagine you have a robot butler. You want it to make you breakfast. But you can't just say "make breakfast" - the robot doesn't understand English!

You need to give it very specific instructions:

  1. Go to the refrigerator
  2. Open the door
  3. Pick up 2 eggs
  4. Close the door
  5. Walk to the stove...

Python is the language we use to give these instructions to computers!

🤖👨‍🍳

Your robot butler needs step-by-step instructions in a language it understands!

Python was created by Guido van Rossum in 1991

He named it after "Monty Python's Flying Circus" (a comedy show, not the snake! 🐍)

Python is designed to be:

  • Easy to read - Code looks almost like English
  • Easy to write - Less typing than other languages
  • Powerful - Can do AI, web apps, games, and more!

Three Important Terms to Understand

1. Interpreted Language

Real-Life Analogy: Think of a UN translator. When someone speaks French, the translator converts it to English line by line, in real-time. They don't wait for the entire speech!

Python works the same way - it reads your code one line at a time and executes it immediately.

2. Object-Oriented Programming (OOP)

Real-Life Analogy: Think of a car. A car has:

  • Properties (data): color, model, speed
  • Actions (behaviors): start, stop, accelerate

In Python, we can create "objects" that bundle data and actions together!

3. High-Level Language

Real-Life Analogy: When you drive a car, you just press the gas pedal - you don't manually inject fuel into each cylinder!

Python handles all the complex computer operations for you. You focus on what you want, not how the computer does it.

📌 In One Sentence Each (So You Never Forget)

Interpreted = Python runs your code line by line as you go (no separate "compile" step). Object-Oriented = We organize code into "objects" that have data and actions (you'll see this in Session 8). High-Level = You write in human-friendly commands; the computer translates them into machine steps for you.

Popular Python IDEs

IDE = Integrated Development Environment (where you write code)

  • Jupyter Notebook - Great for learning & data science
  • VS Code - Free, powerful, lots of features
  • PyCharm - Professional Python IDE
  • Google Colab - Free, runs in browser, no installation!

🎉 Your Very First Python Program!

Every programmer's journey starts with the famous "Hello, World!" program. Let's write yours!

Python Your first program! 
print("Hello, World!")
Output
Hello, World!

Let's Break This Down:

1
print

This is a function - a built-in command that Python understands. Think of it as a megaphone 📢 that displays whatever you give it.

2
( )

Parentheses tell Python: "Here comes the input for this function!" Functions always need parentheses.

3
"Hello, World!"

Text inside quotes is called a "string". Quotes tell Python "this is just text, don't try to interpret it as code."

Why quotes? Without quotes, Python would think Hello is a variable name! Try print(Hello) and you'll get an error because there's no variable called "Hello".

More print() Examples

Python 
# Printing different things
print("I am learning Python!")
print(42)                    # Numbers don't need quotes
print(3.14159)               # Decimals work too
print("The answer is:", 42)  # Multiple items
Output
I am learning Python! 42 3.14159 The answer is: 42
About Comments: Lines starting with # are comments. Python ignores them completely! They're notes for humans reading the code.

📦 Variables: Your Data Storage System

The Moving Day Story

Imagine you're moving to a new house. You pack your things in boxes and label each box:

📦
BOOKS
📦
CLOTHES
📦
KITCHEN

When you need something, you look at the labels to find the right box.

Variables in Python work exactly the same way! They're labeled containers that store data.

Definition: Variable

A variable is a named location in memory used to store data. Variables allow programs to store, retrieve, and manipulate values dynamically.

Python is dynamically typed - you don't need to declare what data type a variable will hold!

Creating a Variable

To create a variable, you need three things:

name = "value"
The label "put inside" What goes in
Python Creating variables 
# Creating variables - like labeling boxes!
name = "Alice"      # Box "name" contains "Alice"
age = 25            # Box "age" contains 25
height = 5.6        # Box "height" contains 5.6
is_student = True   # Box "is_student" contains True

# Python is dynamically typed - no type declaration needed!
growth = 567
Growth = 345        # Different variable! (case sensitive)

🧠 What Happens in Computer Memory:

name
"Alice"
age
25
height
5.6
is_student
True

Using Variables

Python 
# Using variables with print()
print(name)    # Opens the "name" box, shows what's inside
print(age)

# Combine text and variables
print("Hello,", name, "! You are", age, "years old.")
Output
Alice 25 Hello, Alice ! You are 25 years old.
Critical Difference!
  • print("name") → prints the word "name"
  • print(name) → prints what's INSIDE the variable name ("Alice")

Quotes = literal text. No quotes = look up the variable!

The id() Function - Memory Address

Python 
# id() returns the unique memory address of a variable
growth = 567
Growth = 345

print(id(growth))  # Memory location of growth
print(id(Growth))  # Different location! (different variable)
Output
140234567890 140234567920
Why different IDs? growth and Growth are two completely different variables because Python is case-sensitive! They're stored in different memory locations.

📝 Variable Naming Rules: The 7 Golden Rules

The Address Label Story

Imagine writing an address on a package:

  • ✅ "123 Main Street" - Clear and deliverable!
  • ❌ "###@@@!!!" - The postal service would be confused!

Python has similar rules to avoid confusion!

Rule ✅ Correct ❌ Wrong Why?
1. Start with letter or underscore name, _private 1name Numbers first confuse Python
2. Only letters, numbers, underscores my_name2 my-name, any@ Special chars have meanings
3. No spaces allowed machine_learning machine learning Space = end of variable
4. Case sensitive! age ≠ Age ≠ AGE - These are 3 different boxes!
5. No reserved words else1, my_class else, if, for Reserved for Python
6. No special characters data_2025 data), name$ Only _ is allowed
7. Be descriptive student_age x Makes code readable!
Python Valid vs Invalid Names 
# ✅ VALID variable names
hello1 = "how are you"
machine_learning = 45
_year = 2023
aravind = 12345
else1 = 567          # "else1" is fine, "else" is not
t1234 = "tarun"
__DATA = 45

# ❌ INVALID - These will cause errors!
# 1233 = 2024       # Can't start with number
# machine learning = 344  # No spaces!
# data) = 34        # No special chars!
# any@ = 345        # @ not allowed
Python Case Sensitivity Demo 
# These are THREE DIFFERENT variables!
age = 25    # Variable 1
Age = 30    # Variable 2
AGE = 35    # Variable 3

print(age)  
print(Age)  
print(AGE)

print(id(age))
print(id(Age))
print(id(AGE))  # All different memory addresses!
Output
25 30 35 140234567890 140234567920 140234567950

Quick Check: Which are valid variable names?

  • myVariable ✅ Valid - letters only
  • 2nd_place ❌ Invalid - starts with number
  • _secret ✅ Valid - underscore at start is OK
  • user-name ❌ Invalid - hyphen not allowed
  • for ❌ Invalid - reserved word
  • deep_learning45 ✅ Valid - letters, numbers, underscore

🔄 The Assignment Operator (=)

Important: = Does NOT Mean "Equals" in Python!

  • = means "put this value into this variable" (assignment)
  • == means "are these equal?" (comparison)
📦⬅️🎁

Think of = as an arrow pointing LEFT: take the value on the right and PUT IT INTO the variable on the left

Reassigning Variables

Python 
# Variables can change! (That's why they're called "variables")
age = 20
print(age)

age = 21     # Replace the old value with new one
print(age)

age = age + 1  # Take current age, add 1, put result back
print(age)
Output
20 21 22
How does age = age + 1 work?
  1. Look up current value of age → 21
  2. Calculate 21 + 1 → 22
  3. Store 22 back into age

Multiple Assignment - Python's Superpowers! ✨

Python 
# Assign multiple variables at once
rahul, suresh, jhon, tarun = 65, 67, 88, 99
print(jhon)

# Same value to multiple variables
tarun = tanish = tanamyi = 100
print(tanamyi)
Output
88 100
Python The Magic Swap! ✨ 
a = 5
b = 10
print(f"Before: a={a}, b={b}")

# In other languages, you'd need a temporary variable
# Python makes it elegant!
a, b = b, a

print(f"After: a={a}, b={b}")
Output
Before: a=5, b=10 After: a=10, b=5

Python's Elegant Swap

In other languages like C or Java, swapping requires a temporary variable. Python's multiple assignment makes it a one-liner! This is one reason developers love Python.

Type Conversion (Basic)

Python 
age = 56
print(type(age))     # <class 'int'>

age = float(age)     # Convert to float (reallocation)
print(age)
print(type(age))     # <class 'float'>
Output
<class 'int'> 56.0 <class 'float'>

🚫 Common Mistakes (Intro)

💭 Short reflection

In one sentence: why is it useful that Python is interpreted (run line by line) rather than compiled, when you are first learning?

✅ CORE (Must know)

📚 NON-CORE (Good to know)

📋 Session 1 Summary

🐍 Python Is

An interpreted, OOP, high-level language that's easy to learn and powerful!

📦 Variables Are

Named containers that store data. Create with name = value

🖨️ print()

Displays output. Quotes for text, no quotes for variables.

🔍 id()

Returns the memory address of a variable.

📝 Naming Rules

Start with letter/underscore, no spaces, case sensitive!

🔄 Assignment

= puts value in variable. Multiple assignment is powerful!

🎉 Congratulations!

You've completed Session 1! You now know what Python is, how to create variables, and the rules for naming them. You're officially a Python programmer!

Complete code from course notebook: Introduction_to_Python (1).ipynb

Every line of code from the course notebook (verbatim).

# --- Code cell 4 ---
c=123456789234567892345678

# --- Code cell 5 ---
c

# --- Code cell 7 ---
Popular Python IDEs and Editors:
PyCharm:
A comprehensive IDE developed by JetBrains, offering powerful features like intelligent code completion, on-the-fly error checking, debugging, and robust integration with various tools and frameworks. It comes in a free Community Edition and a paid Professional Edition.
Visual Studio Code (VS Code):
A free, open-source code editor from Microsoft, highly extensible through a vast marketplace of extensions. Its Python extension provides excellent features for development, debugging, and linting.
Jupyter Notebook/JupyterLab:
Primarily used for data science and interactive computing, allowing for the creation and sharing of documents containing live code, equations, visualizations, and narrative text.
Spyder:
An open-source IDE specifically designed for scientific computing and data analysis, offering features like a variable explorer, interactive console, and plotting capabilities.
IDLE:
The default IDE bundled with Python, suitable for beginners due to its simplicity and ease of use.
Thonny:
Another beginner-friendly IDE with a clean interface and helpful debugging tools, focusing on ease of learning.
Sublime Text:
A highly customizable and lightweight text editor known for its speed and powerful features, enhanced for Python development via packages.
Atom:
An open-source, hackable text editor developed by GitHub, supporting Python development through various packages.
Eclipse with PyDev:
Eclipse, a popular open-source IDE for multiple languages, can be extended for Python development using the PyDev plugin.
Choosing an IDE:
Beginners:
Thonny or IDLE offer a gentle introduction to Python development.
General-purpose development:
VS Code or PyCharm (Community Edition) provide a robust environment for various projects.
Data Science/Scientific Computing:
Jupyter Notebook/JupyterLab or Spyder are tailored for these specific needs.
Web Development:
PyCharm Professional Edition offers advanced features for web frameworks like Django and Flask.

# --- Code cell 17 ---
a = 2
b = 3
sum = a + b
print(sum)

# --- Code cell 21 ---
a = 15
b = 27
print(f'Before swapping : a, b = {a}, {b}')
a, b = b, a
print(f'After swapping : a, b = {a}, {b}')

Complete code from course notebook: Variables__in_Python (1) (1).ipynb

Every line of code from the course notebook (verbatim).

# --- Code cell 1 ---
# Variable---is a named location in memory used to store data.
# variables allow programs to store,retrieve and manupluate values dynamically.

# --- Code cell 2 ---
# python is a dynamically typed---You need not to define what data type is a variable

# --- Code cell 3 ---
# Defining a variables--Rules
1@ Variable name start with a letters or a underscore(_)
2@ variable can contain alpha-numeric
3@ variable name cannot be an keyword/Reserved words in python (if,else,while,elif,True..)
4@ variable name are case sensitive(Data,DATA and data are different)
5@ Variable name cannot contain spaces
6@ Variable name cannot contain special characters
7@ Variable name should not start with a number

# --- Code cell 4 ---
growth=567

# --- Code cell 5 ---
Growth=345

# --- Code cell 6 ---
Growth

# --- Code cell 7 ---
growth

# --- Code cell 8 ---
id(growth)

# --- Code cell 9 ---
id(Growth)

# --- Code cell 10 ---
_=34563

# --- Code cell 11 ---
_

# --- Code cell 12 ---
hello1="how are you"

# --- Code cell 13 ---
hello1

# --- Code cell 14 ---
elsea=5678

# --- Code cell 15 ---
machine_learning=45

# --- Code cell 16 ---
aravind=12345

# --- Code cell 17 ---
hello=678

# --- Code cell 18 ---
else1=222

# --- Code cell 19 ---
a12=123

# --- Code cell 20 ---
a12=23

# --- Code cell 21 ---
a12

# --- Code cell 22 ---
_=22

# --- Code cell 23 ---
id(_)

# --- Code cell 24 ---
_reeal2345=2025

# --- Code cell 25 ---
reeal2345=67

# --- Code cell 26 ---
else1=7865

# --- Code cell 27 ---
else1

# --- Code cell 28 ---
year=2017

# --- Code cell 29 ---
1233=2024

# --- Code cell 30 ---
import string
spl_char=string.punctuation
print(spl_char)

# --- Code cell 31 ---
_

# --- Code cell 32 ---
45=2033

# --- Code cell 33 ---
year

# --- Code cell 34 ---
=----used for assigning a value
==---used for comparing two values

# --- Code cell 35 ---
year

# --- Code cell 36 ---
_year=2023

# --- Code cell 37 ---
_year

# --- Code cell 38 ---
t1234="tarun"

# --- Code cell 39 ---
t1234

# --- Code cell 40 ---
year

# --- Code cell 41 ---
else1=567

# --- Code cell 42 ---
Else1=567

# --- Code cell 43 ---
id()--used to give identity of any variable

# --- Code cell 44 ---
id(else1)

# --- Code cell 45 ---
id(Else1)

# --- Code cell 46 ---
machine learning=344

# --- Code cell 47 ---
machine_learning=344

# --- Code cell 48 ---
machine_learning

# --- Code cell 49 ---
data)=34

# --- Code cell 50 ---
__DATA=45

# --- Code cell 51 ---
id(DATA)

# --- Code cell 52 ---
id(data)

# --- Code cell 53 ---
id(DATA)

# --- Code cell 54 ---
DATA=45

# --- Code cell 55 ---
DATA

# --- Code cell 56 ---
id(DATA)

# --- Code cell 57 ---
artifical_intelligence=56

# --- Code cell 58 ---
deep_learning45=34.56

# --- Code cell 59 ---
deep_learning45

# --- Code cell 60 ---
machine learning=4.15

# --- Code cell 61 ---
any@=345

# --- Code cell 62 ---
123="rahul"

# --- Code cell 63 ---
a123="rahul"

# --- Code cell 64 ---
# reassigning a variable

# --- Code cell 65 ---
age=20

# --- Code cell 66 ---
age=21   # a variable value can change at any point of time

# --- Code cell 68 ---
# assigning multiple variables in a single line

# --- Code cell 69 ---
rahul,suresh,jhon,tarun=65,67,88,99

# --- Code cell 70 ---
print(jhon)

# --- Code cell 71 ---
# assigning multiple variables of same value

# --- Code cell 72 ---
tarun=tanish=tanamyi=100

# --- Code cell 73 ---
tanamyi

# --- Code cell 74 ---
tarun=tanish=tanamyi=100

# --- Code cell 75 ---
print(tanamyi)

# --- Code cell 76 ---
# Memory allocation in variable assignment

Q--How variables are stored in memory?
A---python stores variables as objects in memory

# --- Code cell 77 ---
The id() function returns a unique id for the specified object.

# --- Code cell 78 ---
age=56

# --- Code cell 79 ---
type(age)

# --- Code cell 80 ---
age=float(age) # reloaction

# --- Code cell 81 ---
age

# --- Code cell 82 ---
type(age)