Python functions

A Function is a set of organized codes that perform a certain task. 

Python functions give a particularity to your programming and a high-level of code reusing (you can use a code more than once in a program).

Defining Your Own Functions

You can define your own function to give the required functionality and re-use them throughout the program. 

Syntax 

def functionname (input parameters or arguments ):
“docstring”
Block of code or indented statements
return [expression]

The two keywords are def (lets the program know that the indented code from the next line onward is part of the function) and return (return an answer from the function)

Example

def printstring( strg ):
   "This is user defined python function to print a string" 
   return

Calling a function

Defining a function just gives it a name, indicates the parameters that are to be included in the function and designs the blocks of code. Immediately the basic structure is finished, you can run it

Function arguments

Here are some of the arguments which can be used to call a function

Required argument: argument placed in correct fixed order. The number of arguments in the function definition should match exactly in the function call. If the function is not matched corrected then there will be an error as the results

def printstring( strg ):
   "This is user defined python function to print a string"
   print (strg)
   return;
we can call this function with the name as follow
printstring()
printstring (“calling second time”)
printstring (“calling third time”)

output

Keyword argument:

In python, when we use keyword argument in a function call then the caller identifies the arguments by its name. Its provides the flexibility to place the arguments out of order as Python interpreter uses the keywords to match the values with parameters

Default argument: assumes a default value if a value is not given in the function call for that argument 

Variable length argument: used to a process a function for more arguments than in the specified functions and they are not usually named name in the function definition. Below is the syntax for a variable length argument.

def functionname([formal_args,] *var_args_tuple ):
“docstring”
Block of code or statements
return [expression]

Anonymous functions.

These are functions which do not use the standard keyword def. instead they are based on the lambda keyword to create small functions.

Lambda can take a numerous number of arguments but return just one as an expression. They are not direct call to print because anonymous function requires an expression. 

Syntax 

lambda [arg1 [,arg2,…..argn]]:expression

Example

# Anonymous function definition is here
sum = lambda arg1, arg2: arg2 - arg2;
call subtract as a function  
print "Value of total : ", subtract( 70, 70 )
print "Value of total : ", subtract( 50, 70 )

Output

The return statement

The return expression return exist a function, optionally given back an expression to the caller. A return expression with no arguments is the same as return none. Below is an example of how you can return a value from a function

def mutiply( arg1, arg2 ):
   total = arg1*arg2
   print "Inside the function : ", total
   return total;
total = multiply( 30, 20 );
print "Outside the function : ", total

output

Scopes of variable

It identifies the portion of the program where you can enter a particular identifier. They are two main types of scope of variables in python which are global and local variables.

Local variables can be accessed only in the inside body of the functions in which they are  found and global variables can be accessed throughout the whole function.

total = 0; # This is global variable.
# Function definition is here
def subtract( arg1, arg2 ):
   # subtract both the parameters and return them."
   total = arg2 - arg1; # Here total is local variable.
   print "Inside the function local total : ", total
   return total;
# Now you can call subtract function
subtract( 40, 70 );
print "Outside the function global total : ", total

Output