Functions_in_Python.pdf text CBSE class 12

 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 -
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.

There are many ways to import a module in
your program, the one's which you should
know are:
Import
From

Import
 It is simplest and most common way to use modules in our code.
 Its syntax is:
 import modulename1 [,modulename2, ---------]
 Example
 >>> import math
 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.
 Example
 >>> value= math.sqrt (25) # dot notation

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 modulename import * ( Import everything from the file)
Example
 >>> from math import sqrt
 value = sqrt (25)

 Python modules are .py files that consist of Python code.
Any Python file can be referenced as a module.
 Some modules are available through the Python Standard
Library and are therefore installed with your Python
installation. Others can be installed with Python’s
package manager pip. Additionally, you can create your
own Python modules since modules are comprised of
Python .py files.

 Writing a module is just like writing any other Python file.
Modules can contain definitions of functions, classes, and
variables that can then be utilized in other Python programs.
To begin, we’ll create a function that prints Hello, World!:
hello.py
# Define a function
def world( ):
print("Hello, World!")
If we run the program on the command line with python hello.py
nothing will happen since we have not told the program to do
anything.

 Let’s create a second file in the same directory called
main_program.py so that we can import the module we just
created, and then call the function. This file needs to be in
the same directory so that Python knows where to find the
module since it’s not a built-in module.
main_program.py
# Import hello module
import hello
# Call function
hello.world()
# or from hello import world

 To append the path of a module to another programming file, you’ll start by importing
the sys module alongside any other modules you wish to use in your main program file.
 The sys module is part of the Python Standard Library and provides system-specific
parameters and functions that you can use in your program to set the path of the
module you wish to implement.
 For example, let’s say we moved the hello.py file and it is now on the path
/usr/sammy/ while the main_program.py file is in another directory.
 In our main_program.py file, we can still import the hello module by importing the sys
module and then appending /usr/sammy/ to the path that Python checks for files.

main_program.py
 import sys
 sys.path.append('/user/sammy/')
 import hello
...
 As long as you correctly set the path for the hello.py
file, you’ll be able to run the main_program.py file
without any errors and receive the same output as above
when hello.py was in the same directory.

Built in Function
Built in functions are the function(s) that
are built into Python and can be accessed
by a programmer.
These are always available and for using
them, we don’t have to import any
module (file).

To define a function keyword def is used
After the keyword comes an identifier i.e. name
of the function, followed by parenthesized list of
parameters and the colon which ends up the line.
Next follows the block of statement(s) that are
the part of function.

def sayHello ( ): # Header
print “Hello World!”
Example-
def area (radius):
a = 3.14*radius**2
returna
Functioncall
>>>printarea (5)

The part of the program where a variable can be used is
known as Scope of variable
Two types of scopes :
● Global Scope
● Local Scope

● With global scope, variable can be used
anywhere in the program
eg:
x=50
def test ( ):
print(“inside test x is “, x)
print(“value of x is “, x)
Output:
inside test x is 50
value of x is 50

● With local scope, variable can be used only within the
function / block that it is created .
Eg:
X=50
def test ( ):
y = 20
print(‘value of x is ’, X, ‘ y is ’ , y)
print(‘value of x is ’, X, ‘ y is ‘ , y)
On executing the code we will get
Value of x is 50 y is 20
The next print statement will produce an error, because the variable y is
not accessible outside the def()

To access global variable inside the function prefix
keyword global with the variable
Eg:
x=50
def test ( ):
global x =5
y =2
print(‘value of x & y inside the function are ‘ , x , y)
Print(‘value of x outside function is ‘ ‘, )
This code will produce following output:
Value of x & y inside the function are 5 2
Value of x outside the function is 5

A default argument is a function parameter that has a default
value provided to it. If the user does not supply a value for this
parameter, the default value will be used. If the user does supply a
value for the default parameter, the user-supplied value is used.
Eg.
def greet (message, times=1):
print message * times
>>> greet (‘Welcome’) # function call with one argument value
>>> greet (‘Hello’, 2) # function call with both the argument values.
Output:
Welcome
HelloHello

 What is the difference between methods, functions & user
defined functions.
 Open help for math module
i. How many functions are there in the module?
ii. Describe how square root of a value may be calculated
without using a math module
iii. What are the two data constants available in math module.

 Create a python module to find the sum and product of digits (separately) and
imports in another program.
 Create a python function to find the a year is leap year of not a leap year
 What is local and global variable? Is global is keyword in python?
 Create a python module to find pow(x,n) and import in another program
 Write a function roll_D ( ), that takes 2 parameters- the no. of sides (with
default
value 6) of a dice, and the number of dice to roll-and generate random roll values
for each dice rolled. Print out each roll and then return one string “That’s all”.
Example roll_D (6, 3)
 4
 1
 6

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