Functions in Python

Python Function is a piece of code or any logic that performs the specific operation. We already saw some Python functions until now, and you may not notice them. For instance, print(), factorial(), round(), etc., are few of the built-in functions in Python programming language.

Let us see the Function definition, declaration, syntax, and example of using functions in Python. There are two types of functions in the Python Programming language:

  • Library Functions: Built-in functions in Python Programming Language called a Library function. We don’t have to bother about the logic inside the Library functions. In our previous articles, We used many library functions such as print(), factorial(), round() etc.
  • User Defined Functions: Instead of relying on built-in functions, Python programming language allows us to create our own functions called as user defined functions. For example, if we want to implement some mathematical calculations, then put them in separate functions with the correct function name. Then we can call that function multiple times.

Advantages of functions in Python

  1. It helps to divide the large programs into small groups so that we can read the code, and debug the program faster and better.
  2. Python Functions stop us from writing the same logic various times. We can bind the logic in one function and then call the same over and over.
  3. Many persons can work on the same program by assigning different functions to each of them.
  4. It encourages us to call the same function with different inputs over multiple times.

Python Functions Syntax

The syntax of the Functions in Python Programming is

def Function_Name (Parameters):
        Local Variable Declaration
        Programming Logic
        Executable Statement 1
        ……
        return
  • def: Keyword def is the introduction to the function definition. Remember, the Python def keyword must immediately follow by Function_Name.
  • Function_Name: It can be any name you wish to give other than the system reserved keywords.
  • Parameters: Every python function accepts 0 or more parameters. It completely depends upon the user requirements.
  • Local Variable Declaration: Sometimes, we may need some temporary variable only for that particular function, then we can declare them inside the function. It is not compulsory, entirely depends upon user requirements. Remember, these variables are available to this particular function only, and we can’t access them outside the function.
  • Logic: Any mathematical or any code or calculations you need to implement in this particular function.
  • Executable Statement: Any print statements to print some data from this particular function.
  • return: This keyword is required to return something from the function. For example, returning the sum of two integers, etc.

User Defined Functions in Python implementation

To implement the user defined functions in the Python program, we have to follow a few rules, such as:

Python Function Declaration

It informs about the function name and number of arguments.

def Function_Name (Parameters):

For example,

def Add(a, b):

Python Function call

Nothing, but calling the original function with a valid number of arguments. For example, Add (2, 3). And remember, User defined function name should exactly match with the calling function.

Python Function Definition

It is the place where we are going to put all the logic, calculations, etc. Please don’t forget the return keyword, otherwise the program not return anything. For example,

def Adding(a, b):
    Sum = a + b
    return Sum
print("After Calling the Function:", Adding(3, 4))

function output

After Calling the Function: 7
>>> Adding(8, 9)
17

Python Function to find Sum and Average of 3 Numbers

In this functions program, the user asked to enter three numbers. Then by calling the function, we calculate the Sum and Average of that three numbers.

# Functions Example
def sumAndAverage(x, y, z):
    Sum = x + y + z
    Average = Sum/3
    print("\n %d is the Total Sum of three Numbers." %Sum)
    print("\n %d is the Average of three Numbers.\n" %Average)
    
# Allows User to enter three values
a = int(input("\nPlease Enter the First Value. a =  "))
b = int(input("\nPlease Enter the Second Value. b =  "))
c = int(input("\nPlease Enter the Third Value. c =  "))

# Calling the Function
sumAndAverage(a, b, c)
sumAndAverage(10, 20, 30)
Functions in Python 2

It is called a function declaration. If you forget this function declaration, then it throws an error.

def sumAndAverage(x, y, z):

The below statements ask the user to enter 3 numbers and store the user input values in a, b, c variables

a = int(input("\nPlease Enter the First Value. a =  "))
b = int(input("\nPlease Enter the Second Value. b =  "))
c = int(input("\nPlease Enter the Third Value. c =  "))

In the next line, we are calling the function multiple times. First, with user-specified values, and then static 10, 20, 30.

sumAndAverage(a, b, c)
sumAndAverage(10, 20, 30)

When it reaches this function, it traverses to check for the sumAndAverage() function. If the function fails to identify the function name, then it throws an error.

Within the Python function,

def sumAndAverage(x, y, z):
    Sum = x + y + z
    Average = Sum/3

We declared 2 local variables, Sum and Average. In the next line, we calculated the sum and average of three numbers using Assignment Operators. Please refer to print(), factorial(), and round() 

Sum = x + y + z
Sum = 10 + 20 + 30 = 60

Average = Sum / 3
Average = 60 / 3 = 20

Prints the sum and average to the output.

 print("\n %d is the Total Sum of three Numbers." %Sum)
 print("\n %d is the Average of three Numbers.\n" %Average)

In the next line, We called Average() one more time, this time, we passed local variables as function arguments. We called 2 times because it helps you to understand that, we can call the function n number of times.