06 Apr 2026

Functions in Python

Defining functions, arguments, return values, scope, and reusable physics calculations.

msc semester-i computational-techniques functions python

A function is a named block of code that performs a task. Functions reduce repetition and make a program easier to test.

Defining a function

def square(x):
    return x * x

print(square(5))

The keyword def begins a function definition. The value after return is sent back to the caller.

Function arguments

Arguments carry data into the function.

def kinetic_energy(mass, velocity):
    return 0.5 * mass * velocity**2

energy = kinetic_energy(2.0, 3.0)
print(energy)

Multiple results

A function can return more than one value by returning a tuple.

def motion(v0, a, t):
    v = v0 + a * t
    s = v0 * t + 0.5 * a * t**2
    return s, v

position, velocity = motion(0.0, 9.8, 2.0)

Local variables

Variables created inside a function are local to that function.

def potential_energy(m, g, h):
    energy = m * g * h
    return energy

The variable energy exists only inside the function body.

Why functions matter

In computational physics, the same formula may be used many times. A function keeps that formula in one place.

def force(k, x):
    return -k * x

This small function can later be used in loops, plots, or numerical integration.