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Lesson Note

Computer Science

Class - XII

Chapter – Working with Functions

Functions
Functions provide a systematic way of problem solving by dividing the given task into several
subtask, finding their individual solution, and integrating the solutions of individual task to solve the
original problem.
Functions can be reused
It makes the program more readable, understandable and makes program management easier.

Python has three types of functions:
i) Built-in functions
ii) Functions defined in Modules
iii) User-defined functions

Built In Functions
These are predefined functions already available in Python. These are always available in standard
library and we don’t have to import any module/file for using them.
Some of the built in functions are: print(), id(), max(), len(), str(), bool(), ord() etc

Modules
As you start to write bigger programs, you'll want to keep the procedure definitions in multiple files,
grouped together according to what they do. So, for example, you might package a set of utility
functions together into a single file, called utility.py. This file is called a module in Python.
Now, if there is a need to use those procedures in another file, or from the the Python shell, just
write/execute the command
import utility
Now, if there is a procedure in that file called sample, to use that in other program command is
utility.sample

User Defined Function

Function defined/created by user
Syntax for a user defined function is:
def function_name (comma separated list of parameters):
statement1
statement2
….
return (optional)

Program without a return statement and not returning any value