🐍 Getting Started with Python

Computers are super fast, but they only understand 0s and 1s. So how do we tell a computer what to do? We write programs in a programming language — and the friendliest one to start with is Python! 🐍 This chapter answers the BIG questions: What is a program and a programming language? Why is Python so popular? How does Python run our code? What are Interactive Mode and Script Mode? And how do we write our very first program? Let's say hello to Python! 👋

2.1 🏁 Introduction — Programs and Languages

A program is a set of step-by-step instructions given to a computer to do a task. Writing these instructions is called programming, and the person who writes them is a programmer.

Analogy: A program is like a recipe 🍳. The recipe tells the cook each step in order — "boil water, add noodles, wait 2 minutes, add masala". A program tells the computer each step in the same way. Miss a step or change the order, and the result goes wrong!

A programming language is a special language with its own words and rules (grammar) that we use to write programs.

2.1.1 Low-Level vs High-Level Languages 🪜

graph TD
    PL["🗣️ PROGRAMMING LANGUAGES"]
    LOW["⚙️ Low-Level Languages\n(close to the machine)"]
    HIGH["🧑 High-Level Languages\n(close to English)"]
    ML["0️⃣1️⃣ Machine Language\n(only 0s and 1s)"]
    AL["🔤 Assembly Language\n(short codes like ADD, MOV)"]
    HL["🐍 Python, Java, C++\n(English-like words)"]

    PL --> LOW
    PL --> HIGH
    LOW --> ML
    LOW --> AL
    HIGH --> HL

    style LOW fill:#795548,color:#fff
    style HIGH fill:#4CAF50,color:#fff

2.1.2 Language Translators 🔄

A computer understands only machine language. So a program written in a high-level language must first be translated into machine language. The software that does this is called a language translator.

Analogy: Suppose you need a speech in Japanese translated. 🇯🇵

• A compiler is like a translator who writes down the translation of the whole speech first, and then hands it over.
• An interpreter is like a translator who stands beside you and translates each sentence as you speak it.

2.2 🐍 What is Python?

Python is a high-level, interpreted, general-purpose programming language that is famous for being simple and easy to read.

Where is Python used? Almost everywhere! 🌍

2.2.1 Features (Advantages) of Python ✅

Look how short a Python program is compared with C++ for the same job:

C++                                        Python
────────────────────────────────           ──────────────────────
#include <iostream>                        print("Hello World")
using namespace std;
int main() {
    cout << "Hello World";
    return 0;
}

2.2.2 Limitations of Python ❌

Nothing is perfect — Python has a few weak points too:

2.3 ⚙️ How Python Runs Your Program

When you run a Python program, the Python interpreter reads it and runs it for you, one line at a time.

graph LR
    A["📝 Your Program\n(hello.py)"]
    B["🐍 Python Interpreter\n(reads line 1, runs it,\nthen line 2, …)"]
    C["🖥️ Output\non the screen"]
    E["❌ Error message\n(if a line is wrong)"]

    A --> B --> C
    B -.-> E

    style B fill:#FF9800,color:#fff
    style C fill:#4CAF50,color:#fff
    style E fill:#F44336,color:#fff

Because Python runs line by line, if line 3 has a mistake, lines 1 and 2 are already done — and Python stops at line 3 with an error message that tells you which line is wrong.

print("Line 1 runs")
print("Line 2 runs")
print("Line 3 runs")

Output:

Line 1 runs
Line 2 runs
Line 3 runs

Fun fact: Behind the scenes, Python first turns your program into a simpler form called bytecode, which is then run by the Python Virtual Machine (PVM). You don't have to do anything for this — it happens automatically!

2.4 🛠️ Working in Python

To write Python programs, we need Python installed on the computer. The free official version from python.org comes with IDLE.

IDLE = Integrated Development and Learning Environment — a simple program where you can type, save and run Python code.

Other popular tools to write Python: Jupyter Notebook, Spyder, VS Code, PyCharm — and the Python Lab on this website! 😊

Python can be used in two modes:

2.4.1 Interactive Mode ⚡

In Interactive Mode, you type one statement at a time after the prompt >>> and Python runs it immediately.

>>> 5 + 3
8
>>> 20 - 7
13
>>> 6 * 4
24
>>> print("I love Python")
I love Python

Analogy: Interactive Mode is like talking to a calculator 🧮 — press the keys, see the answer at once. But once you close it, everything you typed is gone!

• Good for: quick testing, small calculations, checking how a command works.
• Problem: the statements cannot be saved — you have to type them again next time.

To leave the shell, type exit() or quit().

2.4.2 Script Mode 📝

In Script Mode, you write the whole program in the Editor, save it as a file with the .py extension, and then run it.

graph LR
    S1["1️⃣ File → New File"]
    S2["2️⃣ Type the program"]
    S3["3️⃣ File → Save\n(marks.py)"]
    S4["4️⃣ Run → Run Module\n(or press F5)"]
    S5["5️⃣ See output\nin the Shell"]

    S1 --> S2 --> S3 --> S4 --> S5

    style S3 fill:#FF9800,color:#fff
    style S4 fill:#F44336,color:#fff
    style S5 fill:#4CAF50,color:#fff

Code Example: marks.py

# Program to show total marks
print("Report Card")
print("Maths + Science =", 85 + 90)

Output:

Report Card
Maths + Science = 175

Analogy: Script Mode is like writing an essay in your notebook ✍️ — you can save it, read it again, correct it and use it any number of times.

2.5 🖨️ Your First Program — the print() Function

The print() function shows output on the screen. It is the first thing every Python learner uses!

print("Hello, World!")
print("Welcome to Class 11 IP")
print(100)
print(12 + 8)
print("Total =", 12 + 8)

Output:

Hello, World!
Welcome to Class 11 IP
100
20
Total = 20

Comments — anything after a # is a comment. Python ignores it; comments are notes for people reading the code.

# This program greets the user
print("Good Morning!")   # this prints a greeting

Output:

Good Morning!

Code Example: about_me.py

# A small program about me
print("Name   : Aman")
print("Class  : 11")
print("Subject: Informatics Practices")
print("Age next year:", 16 + 1)

Output:

Name   : Aman
Class  : 11
Subject: Informatics Practices
Age next year: 17

⚠️ Common Errors and Misconceptions

🔑 Quick Revision — Exam Ready!

• Program → a set of step-by-step instructions for the computer
• Low-level (machine, assembly) → close to the machine; High-level (Python, Java) → close to English
• Translators → Compiler (whole program at once), Interpreter (line by line), Assembler (assembly → machine)
• Python → created by Guido van Rossum, released in 1991, named after Monty Python's Flying Circus
• Python is → high-level, interpreted, free and open source, portable, case sensitive, dynamically typed, with a huge library
• Limitations → slower than compiled languages, rarely used for mobile apps, some errors show only when the line runs
• Python runs line by line and stops at the first error (internally: bytecode → PVM)
• IDLE → Integrated Development and Learning Environment (Shell + Editor)
• Interactive Mode → >>> prompt, runs immediately, not saved
• Script Mode → .py file, run with F5, saved and reusable
• print() → shows output; text in quotes, numbers without; commas add a space
• # → starts a comment, ignored by Python

🎯 Sample Exam Questions

Q1: Very Short Answer [1 mark each]

a) Who developed Python? Answer: Guido van Rossum

b) What is the extension of a Python program file? Answer: .py

c) Which symbol is the prompt of Python's Interactive Mode? Answer: >>>

d) Which type of translator does Python use? Answer: An interpreter

e) What is the full form of IDLE? Answer: Integrated Development and Learning Environment

f) Which key runs a program in IDLE's Script Mode? Answer: F5

Q2: Short Answer [2 marks]

Differentiate between a high-level and a low-level language.

Answer: A high-level language is close to English, easy to read and write, and works on many types of computers — e.g. Python. A low-level language is close to machine code (0s and 1s or short codes), is hard for people to use, and depends on the type of computer — e.g. assembly language.

Q3: Short Answer [2 marks]

Differentiate between Interactive Mode and Script Mode.

Answer:

Q4: Output Based [2 marks]

Write the output of the following code:

print("Sum is", 15 + 25)
print("15 + 25")
print(100 - 1)

Answer:

Sum is 40
15 + 25
99

Q5: Error Finding [2 marks]

Find and correct the errors in the following code:

Print("Hello")
print("Python')

Answer:

print("Hello")     # print must be in small letters
print("Python")    # quotes must match

Q6: Short Answer [3 marks]

What is an interpreter? Why is Python's interpreter helpful for beginners? Write one limitation of an interpreted language.

Answer: An interpreter is a language translator that translates and runs a program one line at a time. It helps beginners because it stops at the first error and shows the line number, so mistakes are easy to find and correct. Limitation: interpreted programs usually run slower than compiled programs.

✏️ Practice Problems

1. What is a program? Explain with an everyday example other than a recipe.
2. Why must a high-level language program be translated? Name the three types of language translators.
3. Write any four features and two limitations of Python.
4. Why is Python called a platform-independent language?
5. Write the steps to create, save and run a program in IDLE.
6. In Interactive Mode, type 7 + 3, 7 * 3 and 7 - 3. Write the output you get for each.
7. Write a program that prints your name, class and school on three separate lines.
8. Write a program that prints the text Area of rectangle = followed by the result of 12 * 5.
9. Find the output: print("Price:", 50 + 20) and print("50 + 20").
10. Find the error: print(Welcome to Python). Correct it.
11. What is a comment? Write a program with one full-line comment and one comment after a statement.
12. Your friend typed a long program in Interactive Mode and lost it after closing IDLE. Which mode should they have used and why?