Functions in python for beginners part - 1

Functions

Introduction to functions

This article will consist of explaining what a function is in Python and how to create one. Functions will be one of our main building blocks when we construct larger and larger amounts of code to solve problems.

So what is a function?

Formally, a function is a useful device that groups together a set of statements so they can be run more than once. They can also let us specify parameters that can serve as inputs to the functions.

On a more fundamental level, functions allow us to not have to repeatedly write the same code again and again. If you remember back to the lessons on strings and lists, remember that we used a function len() to get the length of a string. Since checking the length of a sequence is a common task you would want to write a function that can do this repeatedly at command.

Functions will be one of the most basic levels of reusing code in Python, and it will also allow us to start thinking of program design (we will dive much deeper into the ideas of design when we learn about Object-Oriented Programming).

def Statements

Let's see how to build out a function's syntax in Python. It has the following form:

def name_of_function(arg1,arg2):
    '''
    This is where the function's Document String (docstring) goes
    '''
    # Do stuff here
    # Return desired result

We begin with def then a space followed by the name of the function. Try to keep names relevant, for example len() is a good name for a length() function. Also, be careful with names, you wouldn't want to call a function the same name as a built-in function in Python (such as len).

Next, comes a pair of parentheses with a number of arguments separated by a comma. These arguments are the inputs for your function. You'll be able to use these inputs in your function and reference them. After this, you put a colon.

Now here is the important step, you must indent to begin the code inside your function correctly. Python makes use of whitespace to organize code. Lots of other programming languages do not do this, so keep that in mind.

Next, you'll see the docstring, this is where you write a basic description of the function. Using iPython and iPython Notebooks, you'll be able to read these docstrings by pressing Shift+Tab after a function name. Docstrings are not necessary for simple functions, but it's good practice to put them in so you or other people can easily understand the code you write.

After all this, you begin writing the code you wish to execute.

The best way to learn functions is by going through examples. So let's try to go through examples that relate back to the various objects and data structures we learned about before.

Example 1: A simple print 'hello' function

def say_hello():
    print('hello')

say_hello()

OUTPUT

hello

Example 2: A simple greeting function

Let's write a function that greets people with their names.

def greeting(name):
    print('Hello %s' %(name))

greeting('Jose')

OUTPUT

Hello Jose

Read Also