02 Apr 2026

Introduction to Python

Variables, statements, comments, input, output, and the structure of a simple Python program.

msc semester-i computational-techniques python

Python is an interpreted programming language. A Python program is a set of instructions written for the computer, but in a form that remains close to ordinary mathematical thinking. It is widely used in computational physics because numerical calculations, plotting, data handling, and symbolic work can be written in a short and readable form.

The first principle is simple: a program stores values, performs operations on them, and displays or saves the result. Variables, expressions, input, output, and indentation are the basic tools for doing this.

Basic structure

A Python program is a sequence of statements. Each statement performs one action.

x = 4
y = 5
z = x + y
print(z)

Here x, y, and z are variables. A variable stores a value and gives it a name.

The equal sign in a program means assignment. The statement x = 4 means “store the value 4 in the name x.” It is not the same as a mathematical equation to be solved.

Comments

Comments are ignored by Python. They are used to explain the purpose of the code.

# speed in metre per second
v = 12.5

Good comments explain the physical meaning, not the obvious syntax.

Input and output

The function print() displays output.

temperature = 300
print("Temperature =", temperature, "K")

The function input() reads text from the keyboard. It gives a string, so numerical input must be converted.

radius = float(input("Enter radius: "))
area = 3.14159 * radius**2
print(area)

Indentation

Python uses indentation to mark blocks of code. A block belongs to a function, conditional, or loop.

if x > 0:
    print("positive")

The indented line runs only when the condition is true.

First complete program

Write a program to calculate the kinetic energy of a body of mass $m$ moving with speed $v$.

The formula is

\[K=\frac12mv^2.\]

mass = float(input("Enter mass in kg: "))
speed = float(input("Enter speed in m/s: "))

kinetic_energy = 0.5 * mass * speed**2

print("Kinetic energy =", kinetic_energy, "J")

If $m=2$ kg and $v=3$ m/s, the output is

Kinetic energy = 9.0 J

This example shows the usual order of a simple program: input, calculation, and output.

Key points

• Python code is read from top to bottom.
• Variables are created when a value is assigned.
• Use meaningful names such as mass, time, and energy.
• Indentation is part of the syntax.

Practice questions

1. What is an interpreted programming language?
2. Write a Python statement to assign the value $3.0$ to a variable named mass.
3. Write a short program to calculate kinetic energy from mass and speed.
4. Why is indentation important in Python?
5. What is the difference between input() and print()?