Functions in Python

 

What is Function in Python:

Function is a code block which is used to perform a specific task. Functions in Python are defined by using ‘def’ keyword which is followed by function name and pair of parenthesis which can have list of parameters.

There are two main categories of functions. One is built-in or library functions and second is user defined functions.

1.    Built-in Functions:

These are the functions which are already available in language. These functions are predefined and precompiled. In Python there are list of built-in functions. Built-in functions are also called as library functions. Following are some built-in functions

Print(), count(), len(), range(), format(), isinstance() etc.

2.    User Defined Functions:

User defined functions are the functions defined by the user. User can give the name of functions as per his choice. These functions are created to perform different tasks.

What are Advantages of Functions:

1.    Reusability of Code:

Once functions are created it can be used inside or outside of program as per requirement for multiple times. This feature helps to avoid writing of same task repeatedly and automatically code writing time, extra memory space can be saved. Reusability of code also help to increase the processing speed.

2.    Decomposition of Program:

Function helps us to decompose our large size program into sub parts or smaller programs. This feature helps to increase the readability of program. This also helps to avoid the complexity of problem.

How to Create Functions in Python:

Syntax:

def function_name(list of arguments):

          function body

          return statement

In the syntax,

def  keyword is used to declare or define the user defined function in Python.

Function_name is the name of the user defined function. The name is given by user. By giving the name to function user has to follow variable declaration rules.

List of arguments are the variables used to perform operations. Through the arguments the values are passed to the function.

: colon is used to terminate the function header.

Body of function contains some valid python statements. All these statements has to be followed by the indentation. Indentation usually means four spaces.

return statement is a statement used to return values to function. Return statement is optional.

 

For Example,

def addition(a,b):   # Function Declaration

    sum=a+b

    return sum      # Function return

In above example def keyword is used to declare the user defined function. Addition is the name of user defined function. In the parenthesis of addition function a,b two arguments are passed. The addition operation is stored in sum variable and this sum variable is returned to the function.

But remember function body has no any effect unless and until you call your function. Statements written in the function will execute unless it is called.

Function Calling:

Syntax:

Function_name( )

function_name  is the name of user defined function it is called.

For example,

Python function to display addition of two numbers

# Function to print addition of two numbers

# Function Declaration

def addition(a,b):        

    sum=a+b

    return sum   # Function return

 

# Function call

result=addition(10,30)  

print("The addition is:",result)

Output:

The addition is: 40

In above program function name is addition with two arguments a and b declared with def keyword. Addition of two variables is stored in sum variable. The sum is returned.

Function is called and two values 10 and 30 are passed in function call. The function call process is stored in result variable.  These two values are given through result variable to the function and result is displayed on screen. The above function is declared with argument and with return.

When function is called the control of program goes to the function definition. The all statements written in function definition are executed.

If we create the functions using the arguments then we have to call the function by passing the values to it.

Function Arguments:

The information can be passed to the function through the arguments. Arguments are declared in function declaration in the parenthesis of function. You can pass as many as arguments as you want but each one of the argument is separated by comma. Arguments are the variables declared in function declaration which takes values to perform the task or operations.

Function with No Argument and No Return Value:

# Function Declaration

def arith():

    add=a+b

    sub=a-b

    mult=a*b

    div=a/b

    mod=a%b

    print("The addition is:",add)

    print("The subtraction is:",sub)

    print("The Multiplication is:",mult)

    print("The division is:",div)

    print("The remainder is:",mod)

 # User Input

a=int(input("Enter first number"))

b=int(input("Enter second number"))

# Function Call

arith()

 

Output:

Enter first number20

Enter second number50

The addition is: 70

The subtraction is: -30

The Multiplication is: 1000

The division is: 0.4

The remainder is: 20

Function With Argument But No Return:

# Function with argument and with no return

def arith(a,b):

    add=a+b

    sub=a-b

    mult=a*b

    div=a/b

    mod=a%b

    print("The addition is:",add)

    print("The subtraction is:",sub)

    print("The Multiplication is:",mult)

    print("The division is:",div)

    print("The remainder is:",mod)

 # User Input

n1=int(input("Enter first number"))

n2=int(input("Enter second number"))

# Function Call

arith(n1,n2)

Output:

Enter first number20

Enter second number30

The addition is: 50

The subtraction is: -10

The Multiplication is: 600

The division is: 0.6666666666666666

The remainder is: 20

  

Function with Argument and With Return:

# Function with argument and with return

def arith(a,b):

    add=a+b

    return add

# User Input

n1=int(input("Enter first number"))

n2=int(input("Enter second number"))

# Function Call

result=arith(n1,n2)

print("The addition is :",result)

Output:

Enter first number20

Enter second number20

The addition is : 40

Function without Argument and with Return

def arith():

    add=a+b

    return add

# User Input

a=int(input("Enter first number"))

b=int(input("Enter second number"))

# Function Call

result=arith()

print("The addition is :",result)

Output:

Enter first number20

Enter second number50

The addition is : 70

Default Argument:

When you call your function without any argument then compiler will take default value for operation that is declared in function declaration.

For example,

def new_function(Name="Rohan"):

    print("My Name is:"+ Name)

   

new_function("Isha")

new_function()

new_function("Sahil")

new_function("Soham")

new_function("Sagar")

Output:

My Name is:Isha

My Name is:Rohan

My Name is:Sahil

My Name is:Soham

My Name is:Sagar

 

In above example new_function is declared with argument name and its value is Rohan. This argument is default argument. The new_function is called with different values but one time it is called it with no argument in this case compiler will take for this function the default argument declared in function declaration i.e. Rohan.

Arbitrary Argument:

When you don’t know about how many values you are going to pass in function call, in this situation we can add * before the parameter name in the function definition. This argument is arbitrary argument.  This will help you to pass as many argument as you want. This will receive tuple of argument and accessed accordingly.

For example,

def new_function(*subjects):

    print("The Subjects are:",subjects )

new_function("DBMS","C++","PHP","Java")

Output:

The Subjects are: ('DBMS', 'C++', 'PHP', 'Java')

In above program new_function is declared with one parameter and before declaring subjects parameter * is used so this is arbitrary argument. This argument will help to pass many values. Through the arbitrary argument compiler will return the tuple arguments.

Keyword Arguments:

If you don’t know about how many keyword arguments are passed in your function you can use keyword arguments i.e. key=value argument by using ** before the keyword argument in the function definition.

For example,

def new_function(**name):

    print("The largest number is:" + name["middle"])

new_function(fname="Sanoya",middle="Manohar",lname="patil")

Output:

The largest number is:Manohar

In above example in the new_function parenthesis name argument is used with ** diuble star. So this will help to take many key=value in function call.