Introduction to Python

1. What is Python?

Python is a high-level, interpreted, object-oriented programming language created by Guido van Rossum in 1991. It emphasizes code readability and allows programmers to express concepts in fewer lines of code than other languages like C++ or Java.

Python is widely used in web development, data science, artificial intelligence, machine learning, scientific computing, and education.

2. Key Features of Python

• Simple and Easy to Learn: Python has a clean syntax that reads like English.
• Interpreted: Code is executed line by line, which helps in debugging.
• Platform Independent: Python programs run on Windows, Linux, macOS, etc.
• Free and Open Source: Python can be used and distributed freely.
• High-Level Language: No need to manage memory or CPU details.
• Object-Oriented: Supports classes, objects, inheritance, and polymorphism.
• Extensive Library Support: Thousands of built-in modules for various tasks.
• Dynamic Typing: Variable types are determined at runtime.
• Large Community: Active community provides support and resources.

3. History of Python

4. Installing Python

To install Python: (1) Visit python.org and download the latest version. (2) Run the installer. (3) Check "Add Python to PATH" during installation. (4) Verify installation by opening a terminal and typing python --version.

For CBSE Class 11, any Python 3.x version is suitable. Python 3.12+ is recommended.

5. Working Modes - Interactive and Script

Python can be used in two modes:

6. Python IDLE

IDLE (Integrated Development and Learning Environment) is Python's built-in IDE. It provides:

• Interactive interpreter with syntax highlighting.
• File editor for writing scripts.
• Debugger for finding errors.
• Auto-completion and indentation support.

7. Your First Python Program

# Program to print Hello World
print("Hello, World!")

# Output: Hello, World!

The print() function displays text on the screen. To run this program: Save it as hello.py and run python hello.py in the terminal.

8. Comments in Python

Comments are used to explain code and are ignored by the interpreter.

# This is a single-line comment

"""
This is a multi-line comment
using triple quotes.
"""

Use comments to document your code, explain complex logic, and temporarily disable code.

9. Indentation in Python

Indentation is Python's way of grouping statements in blocks. Unlike other languages that use braces {}, Python uses whitespace (typically 4 spaces).

if 5 > 2:
    print("Five is greater than two!")  # Indented block

Inconsistent indentation causes IndentationError. Always use consistent spacing.

10. Python Keywords

Keywords are reserved words that have special meaning in Python. There are 35 keywords in Python 3.12.

False, None, True, and, as, assert, async, await, break, class,
continue, def, del, elif, else, except, finally, for, from, global,
if, import, in, is, lambda, nonlocal, not, or, pass, raise,
return, try, while, with, yield

Keywords cannot be used as variable names, function names, or identifiers.

11. Built-in Functions

Python has many built-in functions available without importing any module.

12. Common Errors in Python

13. Best Practices

• Use 4 spaces for indentation (not tabs).
• Use meaningful variable names.
• Add comments to explain complex logic.
• Keep lines under 79 characters.
• Use lowercase with underscores for variable names (snake_case).
• Regularly save and test your code.
• Use the script mode for larger programs.