Python Functions

What are Functions?

A function is a small piece of code that aims to perform a particular task. Functions take an argument as an input and return an output after completing some set of actions on the input. Functions, once defined, can be called numerous times without defining them again and again. Thus, functions make the code reusable.

How to define a function in Python?

In Python, a function can be defined by making use of def keyword. We then specify a function name and write the function code after putting a colon ":" after the function name. Like this

			

def firstPythonFunction():       #Defining a Function
   print("First Python function executed")
  
myFunction()        #Calling a Function

				

Output:

MyFunction executed

A function can be defined with the arguments and a return statement, like this

			

def square(num):       #Defining a Function
   return num*num
  
print(square(9))      #Calling a Function

				

Output:

81

If there is no return statement in the function's body, then it returns None.

			

def hello(name):       #Defining a Function
   print("Hello",name)
  
print(hello("John"))      #Calling a Function

				

Output:

Hello John None

Note:-The body of the function must be specified with proper indentation.

Function with multiple arguments

In Python, multiple arguments in the function can be specified by separating each argument with the commas ",".

			

def hello(name, city):       #Defining a Function
   print("Hello",name,"from", city)

hello("John", "San Francisco")      #Calling a Function

				

Output:

Hello John from San Francisco

Optional arguments can be specified for a function. The only thing we need to do is specify the default values for arguments.

			

def hello(name, country="USA"):       #Defining a Function
   print("Hello",name,"from", country)

hello("John", "San Francisco")      #Calling a Function
hello("John")      #Calling a Function

				

Output:

Hello John from San Francisco Hello John from USA

Here you can see, the country argument is optional. If any value is not specified for this argument, the default value "India" will be used. If a value is specified for this argument, the default value gets overwritten by the specified value.

We must define the optional arguments after the non-optional arguments, i.e., all the optional arguments will be on the right hand side of the non-optional arguments. So, something like this can't be done

			

def hello(name, country="USA", age):       #Defining a Function
   print("Hello",name,age,"years old","from", country)

hello("John", "San Francisco", 19)      #Calling a Function

				

Output:

SyntaxError: non-default argument follows default argument

The above example can be corrected like this

			

def hello(name, age,country="USA"):       #Defining a Function
   print("Hello",name,age,"years old","from", country)

hello("John", 22,"San Francisco")      #Calling a Function

				

Output:

Hello John 22 years old from San Francisco

Also, by default, while making a function call, the argument values are assigned to the corresponding argument depending upon the position of the value. Keyword arguments can be used to specify the argument value independent of their position. Like this

			

def hello(name, age,country="USA"):       #Defining a Function
   print("Hello",name,age,"years old","from", country)

hello(country="San Francisco", age=22, name="John")      #Calling a Function

				

Output:

Hello John 22 years old from San Francisco

The keyword name must be exactly same as the argument name spe cified in the function definition.

Docstring in a Function

A Docstring is a description of the function, class, or module. It briefly explains what a function does. It can be specified using the triple quotation strings right after the function definition. Like this

			

def hello(name, age,country="USA"):       #Defining a Function
   '''returns a greet message'''           #Function Docstring
   print("Hello",name,age,"years old","from", country)
hello(country="San Francisco", age=22, name="John")      #Calling a Function

				

Output:

Hello John 22 years old from San Francisco

We can access the Docstring of function using the __doc__ attribute. Like this

			

def hello(name, age,country="India"):       #Defining a Function
   '''returns a greet message'''           #Function Docstring
   print("Hello",name,age,"years old","from", country)

print(hello.__doc__)

				

Output:

returns a greet message

Types of Functions

Functions are basically categorised into two types:

  1. In-built Functions
  2. User-defined Functions

Built-in Functions

There are many built-in functions available in Python. These are:

Function Description
len() Returns the length of an object
abs() Returns absolute value of number
all() Returns True if all the elements in a iterable are True else returns False If iterable is empty then also returns True
any() Returns True if any elements in the iterable is True else returns False If iterable is empty then also returns False
ascii() Returns ASCII representation of an object
bin() Returns Binary representation of an object
bool() Returns True when the argument is True Returns False when the argument is False
bytearray() Returns array having a given size
bytes() Returns immutable array having a given size
hash() Returns hash of the object
getattr() Returns the named attributes of an object
input() Takes input from the standard input in the form of a string
list() Creates a list from the object given. If no argument is provided, it creates an empty list
max() It returns the largest element from an iterable object
min() It returns the smallest element from an iterable object
next() It returns the next element from the iterator
open() It opens a file and also returns a stream fo character.
pow() Returns the number raised to a power
print() Prints the argument to the standard output or a stream
reversed() It returns a reverse iterator for a sequence
set() Creates a set from the object given. If no argument is provided, it creates an empty set
slice() Creates a slice of the object or sequence
sorted() Returns a new list containing the elements of the given list in ascending order
tuple() Creates a tuple from the object given. If no argument is provided, it creates an empty tuple
zip() Returns iterator of tuples
__import__() Imports a module
type() This function returns the type of the given object
callable() Callable function resultsTrue if the object is callable else it is False
chr() This function returns a unicode string of one character with ordinal
classmethod() It changes a function to a class method
compile() Complex source into a code object
complex() Returns complex number with the given real and imaginary parts
dict() Creates a dict from the object given. If argument is not given, it creates an empty dict
enumerate() Returns pairs containing count and values of the iterable argument
range() Returns a sequence of numbers between a given range
filter() It passes all the elements to the given argument function one by one and returns the elements for which the function becomes True.
map() It passes all the elements to a given argument function one by one and the output elements are returned by the argument function
float() Converts a given type to float type
format() Return formatted representation of a value