Defining Functions in python :

Defining Functions in python (Theory)

Functions in Python :

 Definition :  A function is a block of organised and reusable program code  that perform a
                     single , specific and well defined  task.

(1)A function is consist of two main parts 

        1.Function Header

        2.Function Body/statements  

(2) Python allows its programmer to break a code into small small functions each of which can
      be written more or less independently on other 

  Called functions and calling function  :     

funct(1)

def funct(1):     _________________ #body ___________________                           funct(2)

Here funct(1) is "called" function 

 funct(2) is "calling" function 

 code of 1 function can be fully isolate from other as well

Need of function :

1.Dividing the program into separate  well define function facilitates  each function to

   be written and tested separately .this simplifies the process of program development

2.Understanding ,coding and testing multiple separate function are far easier than doing

   same for one huge function  .

3.Code reuse is one of the most prominent reason to use function  .

4.Inbulid Libraries function speed up the program

5.Length of code get reduce 

Syntax :

    Till now we already  deal with some inbuild libraries functions like len(),sqrt().

Besides using built in function user can also define there own functions ,such functions

are called as user define function .As a Python programmer you can write any number of functions in your program ,However to define a function you must have to keep following things in your mind .

1.function start with keyword " def  "

2.this keyword is followed by the function name and parentheses/Brackets ().

3.function name must be unique 

4. After the parentheses : colon must be placed 

5.Arguments/parameters must be pass through parentheses is required 

6.while writing a function indentation should be maintained properly.

7.Syntax :

def function name ():   __________________ ______________________ ______________________ ______________________ ______________________ Statements /body of function

example :

def multi(a , b):

     c=a*b

     print(c)

x=2

b=3

multi(x , y)                            #calling a function 

  

  

NOTE	Before calling a function, user must have to define it .

Function calling :

NOTE	To run a function, user have to call it explicitly  .

syntax: 

                    function name (parameters if exist )

NOTE:

List of variable used in function call is known as actual parameter list , actual parameter 

list may be  variables name , expression or constants .

Key Points :

while calling a function 

1.The function name and the number of argument in function call must be same 

2.parameter's list must be separated by commas " ,"

passing expression as an argument :

               Argument can be pass as an expression to the called function ,in such case 

argument i.e. expression is first evaluated then converted into  the type of formal parameter  

and thenthe  body of a function gets evaluated .

e.g.

def equation(i):                                          # defining a function 

       print(i)                                                 #body

equation(2+3*4)                                         #calling a function 

output = 14 

The Return Statement  :

           In all our function written above ,no where we have used the return statement .But
you will be surprised to know that every function has an implicit return statement as a last
statement in any function body .This implicit return statement return nothing to its caller ,
It's said to return none.

NOTE	None in Python  is same as Null in C  .

NOTE	A return statement with no argument is the same as none   .

Syntax: 

return (expression)
def cube (x):
     return (x*x*x)
n=10
result =cube(n)
print("Cube of ",n,"=",result)

OUTPUT= Cube of  10 = 1000

NOTE	A return statement can not be  used outside function definition  .

NOTE	A return statement  is the last statement of a function and any  statement after that will not get  included into a function definition   .

Example :
def show():
      print("Hello")
      return()
      print("This line will never be display")
show()
print("Good morning ")
output :
Hello
Good morning



 

This is all about basics of  function in Python , and in next article we will discuss about
some more important functions and their algorithm

I hope this article on functions is helpful for you.




                                                                       Thank u 😊