Getting Started with Python

What is Python?

Python is a popular, free, high-level programming language created by Guido van Rossum (released in 1991). Its code looks almost like English, so it is the first language taught in CBSE Classes XI and XII. YouTube, Instagram, NASA and most AI tools use Python.

Features of Python

Installing Python and IDLE

You can also use editors like VS Code, Thonny, PyCharm, or online tools like Google Colab and Jupyter Notebook.

Interactive mode vs script mode

>>> 5 + 3
8
>>> 'Hi' * 3
'HiHiHi'
>>> 22 / 7
3.142857142857143

Your first program

In IDLE choose File → New File, type the lines below, save as hello.py and press F5.

print('Hello, Class XI!')
print('My first Python program')
print(25 + 17)

print() is a built-in function that shows output on the screen. Text must be inside quotes (single '…' or double "…"); numbers and calculations do not need quotes.

More about print()

print() can show many values separated by commas. Two useful options: sep (what to put between values, default a space) and end (what to put at the end, default a new line).

print('Mango', 'Apple', 'Banana')            # sep is a space by default
print('Mango', 'Apple', 'Banana', sep=' | ')
print('Loading', end='...')
print('done')
print()                                      # empty line
print('Rs.', 250 * 3)

Comments

A comment is a note for humans; Python ignores it. A single-line comment starts with #. For longer notes you can use a string in triple quotes '''…''' (called a docstring when it describes a function).

# This program finds the area of a circle
radius = 7          # radius in cm
area = 3.14 * radius * radius
print('Area =', area, 'sq cm')

Keywords

Keywords are reserved words with a special meaning in Python, such as if, for, while, def, True. You cannot use them as variable names.

import keyword
print(len(keyword.kwlist), 'keywords')
print(keyword.kwlist[:10])
print(keyword.iskeyword('for'), keyword.iskeyword('marks'))

Identifiers and naming rules

An identifier is the name we give to a variable, function or class. Rules:

1. Can contain letters (a–z, A–Z), digits (0–9) and underscore _.
2. Must not start with a digit.
3. Cannot be a keyword.
4. No spaces or special symbols like @ $ % - !.
5. Case-sensitive: Total and total are different.

2nd_name = 'Riya'

Use meaningful names: percentage is far better than p when someone else reads your program.

Summary & practice

• Python: easy, free, interpreted, portable, case-sensitive.
• Interactive mode for quick tests; script mode (.py file) for programs.
• print() with sep and end; comments start with #.
• 35 keywords; identifiers cannot start with a digit or be a keyword.