Modular programming and functions

Modular programming and functions

A function is a named sequence of statement(s) that performs a computation. It contains line of code(s) that are executed sequentially from top to bottom by Python interpreter. They are the most important building blocks for any software in Python.

Functions can be categorized as belonging to

i. Modules

ii. Built in

iii. User Defined


A module is a file containing Python definitions (i.e. functions) and statements. Standard library of Python is extended as module(s) to a programmer. Definitions from the module can be used within the code of a program. To use these modules in the program, a programmer needs to import the module. Once you import a module, you can reference (use), any of its functions or variables in your code. There are many ways to import a module in your program, the one‟s which you should know are:

i. import

ii. from


It is simplest and most common way to use modules in our code. Its syntax is:

import modulename1 [,modulename2, ---------]


>>> import math

(i) search for the file „‟.

(ii) Create space where modules definition & variable will be created,

(iii) then execute the statements in the module.

Now the definitions of the module will become part of the code in which the module was imported.

To use/ access/invoke a function, you will specify the module name and name of the function- separated by dot (.). This format is also known as dot notation.


>>> value= math.sqrt (25) # dot notation

The example uses sqrt( ) function of module math to calculate square root of the value provided in parenthesis, and returns the result which is inserted in the value. The expression (variable) written in parenthesis is known as argument (actual argument). It is common to say that the function takes arguments and return the result.

This statement invokes the sqrt ( ) function. We have already seen many function invoke statement(s), such as

>>> type ( )

>>> int ( ), etc.

From Statement

It is used to get a specific function in the code instead of the complete module file. If we know beforehand which function(s), we will be needing, then we may use from. For modules having large no. of functions, it is recommended to use from instead of import.

Its syntax is

>>> from modulename import functionname [, functionname…..]


>>> from math import sqrt

value = sqrt (25)

Here, we are importing sqrt function only, instead of the complete math module. Now sqrt( ) function will be directly referenced to. These two statements are equivalent to previous example.

from modulename import *

will import everything from the file.