Python Functions

Python Functions – Functions are a way of keeping the code organized in a modular fashion. There are lot of benefits in doing so. Some of them are :

  • An action that is required to be performed multiple times during the lifetime of application, could be encapsulated as a function for code re-usability, thus reducing the code length and redundancy.
  • As functions are the result of an organized code, they help in maintenance and following up with the code easily.

Syntax

def statement is used to define a function in python. Following diagram presents the syntax for a function in python, with all the required and optional elements.

Python Functions Syntax - Python Tutorial - www.tutorialkart.com
Python Functions Syntax

Even thought its trivial, but some useful understanding could be drawn from the syntax, like

  • Since Python is a dynamic language, there is no return type mentioned for a function. However, variables of any type or objects could be returned from a function. And whoever is calling the function should be aware of the variable type that could be returned. For this reason, it is always a good practice to have better and in-detail documentation for functions in your application. This helps in a quick and clear understanding of the task a function can do, when working in teams or making a time travel and revisiting the code that is written by you.
  • Parameters which are inputs for the task done by a function, could become optional if the function is always aware about location of data that is required or if the task doesn’t need any. Multiple parameters could be sent as inputs(arguments) to the functions separated by comma(,).
  • Function Name is the identifier for the function. Rest of the program or another programs could call this function using identifier, the function name.
  • Function body is the set of statements that follow the colon(:) symbol in the definition of function. These set of statements collectively make the task(i.e., required action) and is the piece of code that is executed when the function is called.

Python provides many Built-in Functions like print() to print something to output, max() to find the maximum of the numbers passed as arguments to it, and there are many more functions like these which come with the standard python installation. The list of functions may vary from version to version. For a quick view to complete list of Built-in functions in python 3.6.1, visit https://docs.python.org/3/library/functions.html.

Python also provides programmer or developer the ability to code his/her own functions. These are called user defined functions. By following the syntax of python function that is already mentioned above, you could write your own functions required for the specific problem that you chose to solve.

There are many ways you can prepare your user defined function based on the parameters they have been defined with. Following are some of the possible scenarios and the links to them leads to their respective examples provided below.

Example 1 – Python Function

In this example program, we will define a function with the name welcome and accepts no parameters. The function just prints a string to standard console output.

example.py – Python Program

def welcome():
    print('Welcome to www.tutorialkart.com for learning Python.')

welcome()
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Output

Welcome to www.tutorialkart.com for learning Python.

Please note that when we call the function welcome, we are using parenthesis after the function name. Also, we are not passing any argument(s) inside parenthesis, since function definition says that welcome does not accept any arguments.

Example 2 – Python Function with Fixed Number of Parameters.

In this example, we will define a function multiplication with two parameters: num1 and num2.

example.py – Python Program

def multiplication(num1, num2):
    return num1*num2

result=multiplication(12,89)
print(result)
result=multiplication(198,389)
print(result)
result=multiplication(98,56)
print(result)
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Output

1068
77022
5488

When we called multiplication function, we passed two arguments, since the function requires two arguments.

Example 3 – Python Function with Default Value for Parameter

In this example, we will write a function with with two arguments, and a default value for the second argument.

example.py – Python Program

def multiplication(num1,num2=24):
    """num1 takes number
       num2 takes number, if nothing is provided, 24 is taken as default
       multiplication(num1,num2) returns the multiplication of num1 and num2
       Ex: multiplication(2,7) returns 2*7=14
           multiplication(2) returns 2*24=28)"""
    return num1*num2

result=multiplication(12)#num1=12, num2=24 : as no value provided for num2, 24 is taken as default value
print(result)
result=multiplication(198,389)#num1=198, num2=389
print(result)
result=multiplication(98) #num1=98, num2=24
print(result)
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Output

288
77022
2352

Note : default arguments should follow non-default arguments. Failing to do so results in syntax error as shown in the example below :

def multiplication(num1=2,num2):
    """num1 takes number
       num2 takes number, if nothing is provided, 24 is taken as default
       multiplication(num1,num2) returns the multiplication of num1 and num2
       Ex: multiplication(2,7) returns 2*7=14
           multiplication(2) returns 2*24=48)"""
    return num1*num2
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Output

File "/home/arjun/PycharmProjects/PythonTutorial/functions/func_args_default_val_error.py", line 1
    def multiplication(num1=2,num2):
                      ^
SyntaxError: non-default argument follows default argument

Example 4 – Python Function with Arbitrary Number of Arguments

In this example, we will define a function that can accept any number of arguments.

To accept any number of arguments, provide *args as parameter.

example.py – Python Program

def multiplication(*args):
    """multiplication functions works with args as list of numbers
       multiplication() returns the multiplication of list of numbers in args
       Ex: multiplication(2,7,3) returns 2*7*3=42
           multiplication(3,4,4,5) returns 3*4*4*5=240)"""
    result=1
    for i in args:
        result=result*i
    return result

result=multiplication(12,89, 2, 57)
print(result)
result=multiplication(198, 38, 47)
print(result)
result=multiplication(8, 6)
print(result)
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Output

121752
353628
48

Conclusion

In this Python Tutorial of Python Functions, we have learnt what a function is, the syntax for defining a function in python, a basic understanding on the elements presented in syntax, example python programs for some of the possible functions with different kinds of arguments.