# User defined functions

In Python developers have the option of defining their own functions called *user-defined* functions. These *functions* can be written such that they would perform the required task once they’re called.

A **function** is a block of reusable code that is written in order to perform a *specific* task. Functions take the required information to perform a task as the *input parameter(s)*, perform the required *operations* on these parameters, and then they *return* the final answer.

# Syntax

Now let’s discuss the method to write a *user-defined* function below:

# Example

Let’s take a look at an example now.

def Examplefunc(str): #function that outputs the str parameter
  print "The value is", str 
  #no return statement needed in this function

def Multiply(x,y): #function that computes the product of x and y 
  return x*y #returning the product of x and y

#Calling the functions
Examplefunc(9) #9 passed as the parameter)
answer = Multiply(4,2) #4 and 2 passed as the parameters
print "The product of x and y is:",answer

The function `Examplefunc` above takes a *variable* `str` as *parameter* and then *prints* this value. Since it only prints the value there is no need for a `return` command.

The function `Multiply` takes two parameters `x` and `y` as parameters. It then computes the product and uses the `return` statement to return back the answer.

## Calling a function
In *line 9* and *line 10* we are executing the functions by simply calling them and passing the parameters to them. Since `Multiply` function returns a value we store it in the variable `answer` before printing it. 

## Advantages of user-defined functions

The advantages of using *user-defined* functions include:

* Reusable code blocks so they only need to be written once, then they can be used multiple times.

* Useful in writing common tasks to complex business logic.

* Modification as per requirement so there is no need to write separate code for different scenarios in the program.

* Project can be divided into functions, leading to compact and well-defined code.

How to write a function in Python

User-defined functions in Python enable reusable, modular code, enhancing task performance and modification efficiency.