Day 1: Welcome to Python

What You'll Learn Today

What Python is and why it's popular
Setting up your development environment
Creating and running your first program
Using the interactive shell

What is Python?

Python is a programming language created by Guido van Rossum in 1991. Known for its simple and readable syntax, Python is used by beginners and professionals alike across various industries.

Key Features of Python

flowchart TB
    subgraph Python["Python's Key Features"]
        A["Simple Syntax"]
        B["Rich Libraries"]
        C["Cross-Platform"]
        D["Large Community"]
    end

    A --> E["Easy to Learn"]
    B --> F["High Productivity"]
    C --> G["Runs Everywhere"]
    D --> H["Great Support"]

    style Python fill:#3b82f6,color:#fff
    style A fill:#8b5cf6,color:#fff
    style B fill:#8b5cf6,color:#fff
    style C fill:#8b5cf6,color:#fff
    style D fill:#8b5cf6,color:#fff

Feature	Description
Simple Syntax	Natural, English-like structure that's easy for beginners
Rich Libraries	Standard library and packages for virtually any task
Cross-Platform	Same code runs on Windows, macOS, and Linux
Large Community	Easy to find help and resources

What Can You Do with Python?

Python is an extremely versatile language:

Web Development: Django, Flask, FastAPI frameworks
Data Analysis: pandas, NumPy for data processing
Machine Learning & AI: TensorFlow, PyTorch for deep learning
Automation: Scripts to automate everyday tasks
Scientific Computing: Research and computational tasks

Setting Up Your Environment

Installing Python

Windows

Visit python.org
Download the latest version of Python
Run the installer
Important: Check "Add Python to PATH"
Click "Install Now"

macOS

macOS usually comes with Python pre-installed, but we recommend installing the latest version:

# Using Homebrew
brew install python

Or download the installer directly from python.org.

Linux

Most Linux distributions come with Python pre-installed:

# Debian/Ubuntu
sudo apt update
sudo apt install python3

# Fedora
sudo dnf install python3

Verifying Installation

Open your terminal (Command Prompt on Windows) and run:

python --version

python3 --version

You should see output like:

Python 3.12.0

Your First Program: Hello, World!

By tradition, the first program you write displays "Hello, World!" on the screen.

Method 1: Interactive Shell

Type python or python3 in your terminal and press Enter:

$ python3
Python 3.12.0 (main, Oct  2 2023, 00:00:00) [GCC 11.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

The >>> prompt indicates Python is waiting for your command. Type the following and press Enter:

>>> print("Hello, World!")
Hello, World!

Congratulations! You've run your first Python program.

To exit the shell, type exit() or press Ctrl+D (or Ctrl+Z on Windows).

Method 2: Script Files

For more complex programs, save your code in a file.

Open a text editor (VS Code, PyCharm, or Notepad)
Type the following code:

print("Hello, World!")
print("Welcome to Python!")

Save the file as hello.py
Navigate to the file location in your terminal and run:

python3 hello.py

Output:

Hello, World!
Welcome to Python!

Exploring the Interactive Shell

The interactive shell is an incredibly useful tool for learning Python. You can try code instantly and see results.

Using Python as a Calculator

>>> 2 + 3
5
>>> 10 - 4
6
>>> 5 * 3
15
>>> 20 / 4
5.0
>>> 2 ** 10
1024

Operator	Meaning	Example
`+`	Addition	`2 + 3` → `5`
`-`	Subtraction	`10 - 4` → `6`
`*`	Multiplication	`5 * 3` → `15`
`/`	Division	`20 / 4` → `5.0`
`**`	Exponentiation	`2 ** 10` → `1024`
`//`	Floor Division	`7 // 2` → `3`
`%`	Modulus	`7 % 2` → `1`

Working with Strings

>>> "Hello" + " " + "Python"
'Hello Python'
>>> "Python " * 3
'Python Python Python '
>>> len("Hello")
5

Choosing an Editor

To write Python efficiently, choose a suitable code editor.

Recommended Editors

flowchart LR
    subgraph Editors["Editor Options"]
        A["VS Code"]
        B["PyCharm"]
        C["Sublime Text"]
        D["Jupyter Notebook"]
    end

    A --> A1["Free, lightweight, extensible"]
    B --> B1["Python-focused, feature-rich"]
    C --> C1["Fast and simple"]
    D --> D1["Great for data analysis"]

    style Editors fill:#3b82f6,color:#fff
    style A fill:#22c55e,color:#fff

Editor	Features	Recommendation
VS Code	Free, lightweight, rich extensions	★★★★★
PyCharm	Python-dedicated IDE, full-featured	★★★★☆
Sublime Text	Fast and lightweight	★★★☆☆
Jupyter Notebook	Ideal for data analysis & ML	★★★★☆

Setting Up VS Code

Download from code.visualstudio.com
After installation, open the Extensions tab
Search for "Python" and install it
The Python extension provides syntax highlighting and auto-completion

Writing Comments

You can add comments to your programs. Comments explain your code and are ignored by Python.

# This is a comment
print("Hello")  # You can add comments at the end of a line

# Multiple line comments
# use # at the start of each line

Comments help your future self and other developers understand your code.

Summary

Concept	Description
Python	A simple, versatile programming language
Interactive Shell	An interactive environment for immediate code execution
Script File	Code saved with `.py` extension and executed
print()	Function that displays text on the screen
Comments	Notes starting with `#`, ignored by the program

Key Takeaways

Python is beginner-friendly and useful for many applications
The interactive shell lets you quickly test code
Save serious programs in .py files
Use comments to make your code understandable

Practice Exercises

Exercise 1: Basics

Use the interactive shell to calculate:

123 + 456
1000 minus 357
25 to the power of 4

Exercise 2: Hello, World!

Create a new file called greeting.py that displays:

Your name
Today's date
Your favorite programming language

Challenge

Using the print() function, create a program that displays the following ASCII art:

  *
 ***
*****
 ***
  *

References

Next Up: In Day 2, you'll learn about "Variables and Data Types." Discover how to store and manipulate data!