Python3 Functions introduction

Python  Functions

 Functions:

       Function is a group of related statements that perform a specific task.

       Functions helps us to break our program into smaller and modular chunks. As our program grows larger and larger, functions make organized and manageable.

   ** It avoid repetition and makes code reusable.

  Syntax::

  

       def function_name(parameters):

             " " "

      

             Doc String

             " " "

 

             Statement(s)

       1. keyword "def" marks the start of function header

       2. Parameters(arguments) through which we pass values to a function. These are optional

       3. A colon(:) to make the end of function header

       4. Doc string describe what function does. This is optional

       5. "return statement to return a value from the function. This is optional

How function perform :

 Example:

       def print_name(name):

             " " "

             This function prints the name

             " " "

             print("Hello"+str(name))

Function Call

     Once we have defined a function, we can call it from anywhere

       print_name('Sujith')

 output:  Hello Sujith

Doc String

       The first string after the function header is called the docstring and is short for documentation string.

       Although optional, documentation is a good programming practice, always document your code

       Doc string will be written in triple quotes so that docstring can extend up to multiple lines

       print(print_name.__doc__)

       This function prints the name

return Statement

       The return statement is used to exit a function and go back to the place from where it was called.

       Syntax:

                  return [expression]

->  return statement can contain an expression which gets evaluated and the value is returned.

->  if there is no expression in the statement or the return statement itself is not present inside a function, then the function will return None Object

Eg program:

       def get_sum(lst):

             " " "

             This function returns the sum of all the elements in a list

             " " "

             _sum=0

        

             for num in lst:

                   _sum+=num

             return  _sum

       s=get_sum([1,2,3,4])

       print(s)

output: 10

Scope and Life Time of Variables

-> Scope of a variable is the portion of a program where the variable is recognized

-> variable defined inside a function is not visible from outside. Hence, they have a local scope

-> Lifetime of a variable is the period throughout which the variable exists in the memory

-> The lifetime of variable inside a function is as long as the function executes

-> Variable are destroyed once we return from the function.

Example:

       global_var="This is global variable"

       def test_life_time( ):

             " " "

             This function test the life time of a variable

             " " "

             local_var="This is local variable"

             print(local_var)

             print(global_var)

       #calling function

       test_life_time( )

       print(global_var)

       print(local_var)

output:  This is local variable

              This is global variable

              This is global variable

              -----------------------------------------------------------------------

              ---

              NameError

              NameError:  name 'local_var' is not defined

Python program to print Highest Commom Factor (HCF) of two numbers :

       def computeHCF(a, b):

             smaller=b if a>b else a

             hcf=1

             for i in range(1,smaller+1):

                   if(a%i==0) and (b%i==0):

                        hcf=i

             return hcf

       num1=98

       num2=78

       print("H.C.F of {0} and {1} is: {2}" .format(num1, num2, computerHCF(num1,num2)))

 

output:  H.C.F of 98 and 78 is: 2