Python #1 — Introduction & Setting Up

Why Python?

Python is the most-used language for automation, data science, backend APIs, scripting, and AI tooling — not because it's the fastest, but because it's the most readable. You spend more time thinking about the problem than fighting the syntax.

A few things Python does differently from Java or JavaScript:

• No semicolons — newlines end statements
• Indentation is syntax — blocks are defined by indentation, not curly braces
• Dynamic typing — no type declarations required (optional type hints exist)
• The REPL — run code line by line interactively

Installing Python the Right Way

Don't use the system Python (/usr/bin/python). Use pyenv to manage versions cleanly.

macOS / Linux:

# Install pyenv
curl https://pyenv.run | bash

# Add to your shell config (~/.zshrc or ~/.bashrc)
export PYENV_ROOT="$HOME/.pyenv"
export PATH="$PYENV_ROOT/bin:$PATH"
eval "$(pyenv init -)"

# Restart your shell, then:
pyenv install 3.12.3
pyenv global 3.12.3

python --version   # Python 3.12.3

Windows: Download from python.org — check "Add Python to PATH" during install. Or use pyenv-win.

Verify:

python --version    # Python 3.12.x
pip --version       # pip 24.x

The Python REPL

Python has an interactive shell. Type python in your terminal:

>>> 2 + 2
4
>>> name = "Rupa"
>>> f"Hello, {name}!"
'Hello, Rupa!'
>>> type(name)
<class 'str'>
>>> exit()

Use the REPL constantly while learning. It gives you instant feedback.

Your First Program

Save as hello.py and run:

python hello.py

Notice:

• No class required — Python code can live at the top level
• print() is a function call with parentheses (unlike Java's System.out.println)
• f-strings (f"Hello, {name}!") are the modern way to embed variables in strings

Setting Up VS Code

1. Install VS Code
2. Install the Python extension by Microsoft
3. Install Pylance for type checking and autocompletion
4. Open a .py file — VS Code detects Python and activates

Useful settings (settings.json):

{
  "python.defaultInterpreterPath": "${workspaceFolder}/.venv/bin/python",
  "editor.formatOnSave": true,
  "[python]": {
    "editor.defaultFormatter": "ms-python.black-formatter"
  }
}

Install the Black formatter:

pip install black

Virtual Environments — Always Use One

A virtual environment isolates your project's dependencies. Never install packages globally.

# Create a virtual environment
python -m venv .venv

# Activate it
source .venv/bin/activate      # macOS/Linux
.venv\Scripts\activate         # Windows

# Your prompt changes to show (.venv)
(.venv) $ pip install requests

# Deactivate when done
deactivate

Always add .venv/ to your .gitignore.

# Save your dependencies
pip freeze > requirements.txt

# Restore in another environment
pip install -r requirements.txt

How Python Runs Your Code

your script.py
  → Python reads it line by line
  → Compiles to bytecode (.pyc files in __pycache__)
  → CPython interpreter executes the bytecode

Unlike Java, there's no separate compile step you have to run. python script.py compiles and runs in one command.

What's Next?

Python #2 covers variables, data types, and strings in depth — Python's type system, type hints, and why f-strings are the only string formatting you need to know.