Custom Errors/Exceptions

Python has many built-in exceptions which force your program to output an error when something in it goes wrong. Learn about Raise Custom Errors/Exceptions.

However, sometimes you may need to create custom exceptions that serve your purpose.

In Python, users can define such exceptions by creating a new class. This exception class has to be derived, either directly or indirectly, from Exception class. Most of the built-in exceptions are also derived from this class.

Custom Exception

Here, we have created a user-defined exception called CustomError which is derived from the Exception class. This new exception can be raised, like other exceptions, using the raise statement with an optional error message.

class CustomError(Exception):
pass
x = 1
if x == 1:
raise CustomError('This is custom error')

Output:

Traceback (most recent call last):
File "error_custom.py", line 8, in
raise CustomError('This is custom error')
main.CustomError: This is custom error

Catch custom Exception

This example shows how to catch custom Exception

class CustomError(Exception):
pass
try:
raise CustomError('Can you catch me ?')
except CustomError as e:
print ('Catched CustomError :{}'.format(e))
except Exception as e:
print ('Generic exception: {}'.format(e))
Output:

Catched CustomError :Can you catch me ?

Learn more about Custom Errors/Exceptions here.

Must Read Python Interview Questions

• 165+ Python Interview Questions & Answers

200+ Python Tutorials With Coding Examples

Python Language Basics Tutorial	Python String Representations of Class Instances
Python For Beginners Tutorial	Python Debugging Tutorial
Python Data Types Tutorial	Reading and Writing CSV File Using Python
Python Indentation Tutorial	Writing to CSV in Python from String/List
Python Comments and Documentation Tutorial	Python Dynamic Code Execution Tutorial
Python Date And Time Tutorial	Python Code Distributing using Pyinstaller
Python Date Formatting Tutorial	Python Data Visualization Tutorial
Python Enum Tutorial	Python Interpreter Tutorial
Python Set Tutorial	Python Args and Kwargs
Python Mathematical Operators Tutorial	Python Garbage Collection Tutorial
Python Bitwise Operators Tutorial	Python Pickle Data Serialisation
Python Bolean Operators Tutorial	Python Binary Data Tutorial
Python Operator Precedance Tutorial	Python Idioms Tutorial
Python Variable Scope And Binding Tutorial	Python Data Serialization Tutorial
Python Conditionals Tutorial	Python Multiprocessing Tutorial
Python Comparisons Tutorial	Python Multithreading Tutorial
Python Loops Tutorial	Python Processes and Threads
Python Arrays Tutorial	Python Concurrency Tutorial
Python Multidimensional Arrays Tutorial	Python Parallel Computation Tutorial
Python List Tutorial	Python Sockets Module Tutorial
Python List Comprehensions Tutorial	Python Websockets Tutorial
Python List Slicing Tutorial	Sockets Encryption Decryption in Python
Python Grouby() Tutorial	Python Networking Tutorial
Python Linked Lists Tutorial	Python http Server Tutorial
Linked List Node Tutorial	Python Flask Tutorial
Python Filter Tutorial	Introduction to Rabbitmq using Amqpstorm Python
Python Heapq Tutorial	Python Descriptor Tutorial
Python Tuple Tutorial	Python Tempflile Tutorial
Python Basic Input And Output Tutorial	Input Subset and Output External Data Files using Pandas in Python
Python Files And Folders I/O Tutorial	Unzipping Files in Python Tutorial
Python os.path Tutorial	Working with Zip Archives in Python
Python Iterables And Iterators Tutorial	gzip in Python Tutorial
Python Functions Tutorial	Stack in Python Tutorial
Defining Functions With List Arguments In Python	Working with Global Interpreter Lock (GIL)
Functional Programming In Python	Python Deployment Tutorial
Partial Functions In Python	Python Logging Tutorial
Decorators Function In Python	Python Server Sent Events Tutorial
Python Classes Tutorial	Python Web Server Gateway Interface (WSGI)
Python Metaclasses Tutorial	Python Alternatives to Switch Statement
Python String Formatting Tutorial	Python Packing and Unpacking Tutorial
Python String Methods Tutorial	Accessing Python Sourcecode and Bytecode
Using Loops Within Functions In Python	Python Mixins Tutorial
Python Importing Modules Tutorial	Python Attribute Access Tutorial
Difference Betweeb Module And Package In Python	Python Arcpy Tutorial
Python Math Module Tutorial	Python Abstract Base Class Tutorial
Python Complex Math Tutorial	Python Plugin and Extension Classes
Python Collections Module Tutorial	Python Immutable Datatypes Tutorial
Python Operator Module Tutorial	Python Incompatibilities Moving from Python 2 to Python 3
Python JSON Module Tutorial	Python 2to3 Tool Tutorial
Python Sqlite3 Module Tutorial	Non-Official Python implementations
Python os Module Tutorial	Python Abstract Syntax Tree
Python Locale Module Tutorial	Python Unicode and Bytes
Python Itertools Module Tutorial	Python Serial Communication (pyserial)
Python Asyncio Module Tutorial	Neo4j and Cypher using Py2Neo
Python Random Module Tutorial	Basic Curses with Python
Python Functools Module Tutorial	Templates in Python
Python dis Module Tutorial	Python Pillow
Python Base64 Module Tutorial	Python CLI subcommands with precise help output
Python Queue Module Tutorial	Python Database Access
Python Deque Module Tutorial	Connecting Python to SQL Server
Python Webbrowser Module Tutorial	Python and Excel
Python tkinter Tutorial	Python Turtle Graphics
Python pyautogui Module Tutorial	Python Persistence
Python Indexing And Slicing Tutorial	Python Design Patterns
Python Plotting With Matplotlib Tutorial	Python hashlib
Python Graph Tool Tutorial	Creating a Windows Service Using Python
Python Generators Tutorial	Mutable vs Immutable (and Hashable) in Python
Python Reduce Tutorial	Python configparser
Python Map Function Tutorial	Python Optical Character Recognition
Python Exponentiation Tutorial	Python Virtual Environments
Python Searching Tutorial	Python Virtual Environment – virtualenv
Sorting Minimum And Maximum In Python	Python Virtual environment with virtualenvwrapper
Python Print Function Tutorial	Create virtual environment with virtualenvwrapper in windows
Python Regular Expressions Regex Tutorial	Python sys Tutorial
Copying Data In Python Tutorial	ChemPy – Python package
Python Context Managers (“with” Statement) Tutorial	Python pygame
Python Name Special Variable Tutorial	Python pyglet
Checking Path Existence And Permissions In Python	Working with Audio in Python
Creating Python Packages Tutorial	Python pyaudio
Usage of pip Module In Python Tutorial	Python shelve
Python PyPi Package Manager Tutorial	IoT Programming with Python and Raspberry PI
Parsing Command Line Arguments In Python	kivy – Cross-platform Python Framework for NUI Development
Python Subprocess Library Tutorial	Pandas Transform
Python setup.py Tutorial	Python vs. JavaScript
Python Recursion Tutorial	Call Python from C#
Python Type Hints Tutorial	Python Writing Extensions
Python Exceptions Tutorial	Python Lex-Yacc
Raise Custom Exceptions In Python	Python Unit Testing
Python Commonwealth Exceptions Tutorial	Python py.test
Python urllib Tutorial	Python Profiling
Web Scraping With Python Tutorial	Python Speed of Program
Python HTML Parsing Tutorial	Python Performance Optimization
Manipulating XML In Python	Python Security and Cryptography
Python Requests Post Tutorial	Secure Shell Connection in Python
Python Distribution Tutorial	Python Anti Patterns
Python Property Objects Tutorial	Python Common Pitfalls
Python Overloading Tutorial	Python Hidden Features
Python Polymorphism Tutorial	Python For Machine Learning
Python Method Overriding Tutorial	Python Interview Questions And Answers For Experienced
Python User Defined Methods Tutorial	Python Coding Interview Questions And Answers

Other Python Tutorials

• What is Python?
• Python Advantages
• Python For Beginners
• Python For Machine Learning
• Machine Learning For Beginners
• 130+ Python Projects With Source Code On GitHub