Skip to content

Introduction to python.md

Latest commit

 

History

History
175 lines (121 loc) · 5.89 KB

Introduction to python.md

File metadata and controls

175 lines (121 loc) · 5.89 KB
Raw

Introduction to Python

Notes for Part 1 of the course. Theory kept short and practical — only what you actually need to know.

1. What is Python?

Python is a high-level, general-purpose programming language used to build software and automate tasks.

  • High-level → the code is written in a way that is close to plain English, so it is easy for humans to read and write. You don't manage memory, pointers, or CPU registers yourself.
  • General-purpose → not tied to one field. The same language works for websites, data, AI, testing, and scripts.
  • Simple, readable syntax → this is the main reason Python is easy to learn. Fewer symbols, fewer rules, less boilerplate.

Created by Guido van Rossum, first released in 1991. The version used today is Python 3.

2. Why Learn Python?

Python is used across many areas:

Area What Python is used for
Web development Building websites and web apps (Django, Flask)
Backend development Server-side logic and APIs (FastAPI)
Automation & scripting Automating repetitive daily tasks
Data analysis Cleaning and analysing data (Pandas, NumPy)
Data engineering Building data pipelines
AI & Machine Learning Models and deep learning (scikit-learn, PyTorch)
Web scraping Pulling data from websites (BeautifulSoup, Selenium)
Testing Automated test scripts (PyTest, Selenium)

Must know: one language, many career paths. That is why it is usually the first language recommended.

3. Python Installation

  1. Go to https://www.python.org/downloads/
  2. Download the latest Python 3 version for your OS.
  3. On Windows, tick "Add Python to PATH" during installation. This step is easy to miss and causes most "python is not recognized" errors.
  4. Verify in the terminal:
python --version      # Windows
python3 --version     # macOS / Linux

If a version number prints, Python is installed correctly.

4. VS Code Installation

VS Code is the editor (where you write code). Python is the language (what runs the code). You need both.

  1. Download from https://code.visualstudio.com/
  2. Install it.
  3. Open the Extensions panel and install the Python extension by Microsoft.
  4. Select your interpreter: Ctrl + Shift + P / Cmd + Shift + P → Python: Select Interpreter → pick the Python you installed.

5. Running Your First Python Program

Create a file ending in .py, for example Part_1.py:

print("Hello Welcome to my channel")

Run it:

python Part_1.py      # Windows
python3 Part_1.py     # macOS / Linux

Or press the Run (▶) button in VS Code.

print() is a built-in function that displays whatever you put inside the brackets on the screen.

6. Comments

Comments are notes for humans. Python ignores them completely when running the code.

Single-line comment — #

# Adding two numbers and storing in result
a = 12
b = 13
result = a + b
# print(result)

Shortcut to comment/uncomment a line: Ctrl + / (Windows) or Cmd + / (macOS).

Multi-line comment block — ''' or """

'''
    This is my comment block
    this is vivek pandey
'''

Why comments matter: they explain why the code does something. Code shows what happens; comments explain the reason. Also useful to temporarily disable a line while testing.

7. How Python Works Internally

This is the part most beginners skip, but it explains a lot of Python's behaviour.

The flow

Python Code (.py)
      ↓
Python Compiler
      ↓
Bytecode (.pyc)
      ↓
PVM  (Python Virtual Machine)
      ↓
Machine-level execution
      ↓
CPU

What each step does

Step What happens
Python Code The .py file you wrote — plain, human-readable text.
Python Compiler Converts your source code into bytecode. It also catches syntax errors here, before anything runs.
Bytecode A low-level, platform-independent set of instructions. Not machine code, not readable Python. Cached in a __pycache__ folder as .pyc files so the same file doesn't get recompiled every time.
PVM (Python Virtual Machine) The engine that understands and executes the bytecode, one instruction at a time. This is the actual "interpreter" part of Python.
Machine-level execution The PVM translates each bytecode instruction into operations the machine can perform.
CPU Executes the machine instructions produced by the PVM and returns the result.

Things worth remembering

  • Python is both compiled and interpreted. Compiled to bytecode, then interpreted by the PVM. So the common line "Python is an interpreted language" is only half the story.
  • You never compile manually. Unlike C or Java, this happens automatically every time you run the file.
  • Bytecode is portable, the PVM is not. The same .pyc runs anywhere, but each OS needs its own Python installation. This is what makes Python platform-independent.
  • This extra layer costs speed. Python is slower than C because of the PVM step in the middle. In return you get readability and speed of development.
  • CPython is the standard implementation (written in C) — that's what you get from python.org. Other implementations exist: PyPy (faster), Jython (runs on the JVM), IronPython (.NET).

See the bytecode yourself

import dis

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

dis.dis(add)

This prints the actual bytecode instructions the PVM will run. Useful once, just to make the concept concrete.

Quick Recap

  • Python is high-level, general-purpose, and readable.
  • It is used in web, backend, automation, data, AI, scraping, and testing.
  • Install Python first, then VS Code, then the Python extension.
  • print() displays output; # and '''...''' create comments.
  • Your code is compiled to bytecode, and the PVM runs that bytecode on the CPU.