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What are the Different Types of Python Functions: Explained with Syntax

Date: 27-03-2023

Python is a widely-used programming language that has a variety of built-in functions and libraries that make it a powerful tool for developers.

Functions are one of the fundamental building blocks of any programming language, and Python is no exception. Python functions can be broadly classified into two categories: pre-defined functions and user-defined functions.

In this blog, we will explore the differences between these two types of functions and how they are used in Python programming. Let’s begin by understanding what are the two key types of python functions.

Types of Functions

In this blog, we will be talking about the following two types of python functions.

  1. Pre-defined functions (Inbuilt/Library function)
  2. User-defined functions (Custom function)

Pre-defined Functions

Pre-defined functions, also known as built-in functions, are functions that come pre-packaged with Python. These functions are already implemented in the language, so you can use them without having to write any code. Some examples of pre-defined functions in Python include print(), input(), len(), and range().

Python also comes with a vast collection of libraries that provide additional pre-defined functions for developers. These libraries include NumPy, Pandas, Matplotlib, and many others. Each library provides a set of functions that are designed to solve specific problems, such as data analysis, data visualization, or machine learning.

Predefined functions examples

print(), len(), str() etc

User-defined Functions

User-defined functions, also known as custom functions, are functions that you create yourself. These functions can be used to perform a specific task or set of tasks that you define. User-defined functions are written in Python and can be called from anywhere in your code.

To create a user-defined function in Python, you must first define the function using the def keyword, followed by the function name, and any parameters the function requires. Once the function is defined, you can call it from anywhere in your code by using its name and passing in any necessary arguments.

User-defined functions examples

printsum(a,b), printName(“name”) etc

Need of Functions

There is always a great need for functions in python, below I have listed the top 3 crucial reasons why we need functions.

  1. Reduce complexity
  2. DRY – Don’t repeat yourself
  3. Code reusability 

Syntax of a Function in Python

def function_name(parameters) -> return_type:
      More statements

Explanation of Function Syntax


Here the def keyword is used to mark that the following code is part of the definition of a function and certain rules will be followed here. 


The function_name is defined by which the function so created will be called. 


A function can have n number of arguments passed to it where n can vary between 0 to any greater number. Parameters can be of named and not named type.


The return type is an optional part where if we don’t want the function to return any specific type then we don’t need to define it. But if we want to make the function return a specific type of value then we should define the return type which binds the function to return only the specific type value otherwise it will return an exception.


The function body is the part where the code for the operation that the function will perform is defined. It can be a single line or multiple lines. 

Different Types of Methods

  1. Method without params
  2. Method with known number of  params
  3. Method with unknown number of params
  4. Method with Keyword Arguments
  5. Method with unknown number of Keyword Arguments

The method without params: 

This is the method in which no argument is in requirement to carry out the operation/code that has to execute.  Eg method returning current DateTime.

def get_current_date_time():
              return current_date_time

Here sending any argument doesn’t make any sense so this method is without arguments

The method with a known number of Parameters

This is the method where it is beforehand known how many parameters will be passed and have to be operated upon to return the required response. Like in the case of returning the full name function. 

def get_customer_full_name(f_name, l_name):
              return f_name+” ”+l_name

Here we know how many params we will be sending and defining beforehand to return the required response. 

The method with an unknown number of Params

Methods where the number of arguments is not-define beforehand and can vary in such cases we define the arguments with an * sign before the argument name and it will convert the params into a tuple of params. Like in the case of a function returning the average of numbers passed to it. 

def averages(*numbers):
              sum = 0
              num = len(numbers)
              for num in numbers:
                             sum = sum + num
              return sum/num

Here we can pass any number of arguments, eg 2 or 20 and it will return us an average of the numbers passed to this function. 

The method with Keyword Arguments

Method where the arguments are passing as key and value. In these methods, the order of params does not matter. 

def myfunc(arg1, arg2, arg3):
              print(f”arg1: {arg1}, arg2: {arg2}, arg3: {arg3}”)
myfunc(arg3=”three”, arg1=”First”, arg2=”Two”)

Here the order of argument does not matter. 

The method with an unknown number of Keyword Arguments: 

Method where there is a number of arguments but the number is unspecified or unknown at the time of definition and uses keyword arguments in those cases we can add **(double asterisk) before the parameter name to handle the list of named parameters, for example:

def displayInfo(**userdetail):
              print(f“Welcome {userdetail[first_name]}” )
print(f“Full Name: {userdetail[first_name]} {userdetail[last_name]}” )
displayInfo(first_name = “John”, middle_name = “Doe”, last_name = “Water”)

Special Types of Functions

The following are some of the special types of functions in the python programming language:

  1. Magic functions
  2. Recursive functions
  3. Lambda functions


Python functions are an essential component of any Python program. Pre-defined functions are functions that come built-in with Python, while user-defined functions are functions that you create yourself. Pre-defined functions provide a powerful set of tools that you can use to solve a wide range of problems, while user-defined functions allow you to create custom functionality tailored to your specific needs.

Understanding the differences between these two types of functions and how they are in use in Python programming is crucial for any developer looking to build robust and efficient applications. By leveraging the power of pre-defined functions and creating custom user-defined functions, you can create powerful and flexible applications that can tackle a wide range of challenges.

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