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Python Concepts for Data Science: Python Functions

Function in any programming language is a sequence of statements in a certain order, given a name. When called, those statements are executed. So we don’t have to write the code again and again for each [type of] data that we want to apply it to. This is called code re-usability.

Python lets us group a sequence of statements into a single entity, called a function. A python function may or may not have a name.

Rules for naming python function (identifier)

We follow the same rules when naming a function as we do when naming a variable.

  1. It can begin with either of the following: A-Z, a-z, and underscore(_).

  2. The rest of it can contain either of the following: A-Z, a-z, digits(0-9), and underscore(_).

  3. A reserved keyword may not be chosen as an identifier.

Types of Functions in Python

1. User-Defined Function

User-defined functions in python are the functions that are defined or customized to perform certain specific tasks.

1.1 Advantages of User-defined Functions

  • Python Function help divide a program into modules. This makes the code easier to manage, debug, and scale.

  • It allows function reuse. Every time we need to execute a sequence of statements, all we need to do is to call the function.

  • It allows us to change functionality easily, and different programmers can work on different functions.

Defining a Function

  • To define our own Python function, we use the ‘def’ keyword before its name. And its name is to be followed by parentheses, before a colon(:).

  • Example1: Defining a Function

 def hello():

Note: The contents inside the body of the function must be equally indented.

Calling a Function

  • To call a Python function at a place in our code, we simply need to name it, and pass arguments, if any. Let’s call the function hello() that we defined in defining a function.

  • Example 2: Calling a Function


Functions with Parameter

  • Sometimes, we may want a function to operate on some variables, and produce a result. Such a function may take any number of parameters. Let’s take a function to add two numbers.

  • Example 3: Function with Parameter

def sum(a,b):

Here, the function sum() takes two parameters- a and b. When we call the function, we pass numbers 2 and 3. These are the arguments that fit a and b respectively. We will describe calling a function in point f. A function in Python may contain any number of parameters, or none.

  • Example 3a: Adding two parameter in two different datatype i.e. integer and float.

def sum2(a,b):

Note: We can't add two incompatible type.

  • Example 3b: Adding two incompatible type



Python Return Function

  • A Python function may optionally return a value. This value can be a result that it produced on its execution. Or it can be something you specify, an expression or a value.

  • Example 4: Returning in a Function

def func1(a):
    if a%2==0:
        return 0
        return 1


Deleting Python Function

  • We can delete a function with the ‘del’ keyword.

  • Example 5: Deleting a Function

2. Built-In Function

  • In-built functions in Python are the in-built codes for direct use. For example, print() function prints the given object to the standard output device .

  • In Python 3.9 (latest version), there are 69 built-in functions. Some of the commonly used in-built functions in Python are:




returns the absolute value of a number


returns true when all elements in iterable are true


Returns String Containing Printable Representation


​Formats a specified value

  • Example 6: Built-In Function in Python

x = [1,2,3,4,5]
print(len(x))   # it return length of list
print(type(x))  # it return object type

3. Python Recursive Function

  • A very interesting concept in any field, recursion is using something to define itself. In other words, it is something calling itself.

  • In Python function, recursion is when a function calls itself. To see how this could be useful, let’s try calculating the factorial of a number. Mathematically, a number’s factorial is:


  • Example 7: Recursive Function in Python

def facto(n):
  if n==1:
    return 1
  return n*facto(n-1)


In this article we learned about the Python function. First, we saw the advantages of a user-defined function in Python. Then, we can studied create, update, and delete a function. We also learned that a function may take arguments and may return a value.

Hence we can conclude that, functions is the core building blocks of any programming language that a programmer must learn to use. Python provides a large number of in-built methods for direct use and also allows us to define our custom functions.

Thank you for our time! Enjoy reading.


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