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here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta python exception class Discuss the workings and policies of this site About Us Learn python raise valueerror more about Stack Overflow the company Business Learn more about hiring developers or posting ads with us syntax for generic except clause in python Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, python raise exception with message helping each other. Join them; it only takes a minute: Sign up Manually raising (throwing) an exception in Python up vote 800 down vote favorite 189 How can I raise an exception in Python so that it can later be caught via an except block? python exception exception-handling share|improve this question edited Feb 3 '15 at 14:37

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DavidRR 5,20472747 asked Jan 12 '10 at 21:07 TIMEX 41.2k201525826 add a comment| 3 Answers 3 active oldest votes up vote 787 down vote accepted How do I manually throw/raise an exception in Python? Use the most specific Exception constructor that semantically fits your issue. Be specific in your message, e.g.: raise ValueError('A very specific bad thing happened') Don't do this: Avoid raising a generic Exception, to catch it, you'll have to catch all other more specific exceptions that subclass it. Hiding bugs raise Exception('I know Python!') # don't, if you catch, likely to hide bugs. For example: def demo_bad_catch(): try: raise ValueError('represents a hidden bug, do not catch this') raise Exception('This is the exception you expect to handle') except Exception as error: print('caught this error: ' + repr(error)) >>> demo_bad_catch() caught this error: ValueError('represents a hidden bug, do not catch this',) Won't catch and more specific catches won't catch the general exception: def demo_no_catch(): try: raise Exception('general exceptions not caught by specific handling') except ValueError as e: print('w

you have probably seen some. There are (at least) two distinguishable kinds of errors: syntax errors and exceptions. 8.1. Syntax Errors¶ Syntax errors, also known as parsing errors, are perhaps the most common kind of complaint you get while you

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are still learning Python: >>> while True print 'Hello world' File "", line 1 while python custom exception best practices True print 'Hello world' ^ SyntaxError: invalid syntax The parser repeats the offending line and displays a little ‘arrow' pointing at the earliest point is nested try block possible in python in the line where the error was detected. The error is caused by (or at least detected at) the token preceding the arrow: in the example, the error is detected at the keyword print, since a colon http://stackoverflow.com/questions/2052390/manually-raising-throwing-an-exception-in-python (':') is missing before it. File name and line number are printed so you know where to look in case the input came from a script. 8.2. Exceptions¶ Even if a statement or expression is syntactically correct, it may cause an error when an attempt is made to execute it. Errors detected during execution are called exceptions and are not unconditionally fatal: you will soon learn how to handle them in Python programs. Most exceptions are https://docs.python.org/2.7/tutorial/errors.html not handled by programs, however, and result in error messages as shown here: >>> 10 * (1/0) Traceback (most recent call last): File "", line 1, in ZeroDivisionError: integer division or modulo by zero >>> 4 + spam*3 Traceback (most recent call last): File "", line 1, in NameError: name 'spam' is not defined >>> '2' + 2 Traceback (most recent call last): File "", line 1, in TypeError: cannot concatenate 'str' and 'int' objects The last line of the error message indicates what happened. Exceptions come in different types, and the type is printed as part of the message: the types in the example are ZeroDivisionError, NameError and TypeError. The string printed as the exception type is the name of the built-in exception that occurred. This is true for all built-in exceptions, but need not be true for user-defined exceptions (although it is a useful convention). Standard exception names are built-in identifiers (not reserved keywords). The rest of the line provides detail based on the type of exception and what caused it. The preceding part of the error message shows the context where the exception happened, in the form of a stack traceback. In general it contains a stack traceback listing source lines; however, it will not display lines read from standard input. Built-in Exceptions lists the built-in exceptions and their meanings.

Java C# C++ Go C .NET Haskell Perl Erlang Matlab Debugging Crystal Mobile App Programming Mobile App Programming iOS Android Swift PhoneGap Cordova https://www.codementor.io/python/tutorial/how-to-write-python-custom-exceptions Ionic Titanium Sencha Design / UX Design / UX HTML/CSS CSS Sass Twitter bootstrap Famo.us Kendo UI Responsive design Foundation Photoshop Database / Operations Database / Operations Server DevOps MySQL SQL MongoDB Hadoop Apache Linux AWS Heroku Database Security Azure Development Process / Tools Development Process / Tools Git DevOps WordPress Drupal Joomla SEO Vim Bower python raise Machine learning Xcode Jenkins Top Developers Top Developers Ruby Javascript AngularJS Python iOS Swift PHP Java Programming Tutors Programming Tutors Java C# Python Computer Science Live Classes Learn to Code Live Classes Live Classes Machine Learning 10/20 React and Redux - 10/26 Beginner Python - 11/3 Beginner React - 11/3 Build a WhatsApp Clone - clause in python 11/7 JavaScript - 11/7 Beginner Angular 2 - 10/13 Node.js - 10/12 Beginner AngularJS Video Course ES6 React Native Full Stack Web Dev Online Coding Courses Online Coding Courses Web Development Ruby on Rails Swift AngularJS Python Learning Center Hire CodementorX Gigs Web Development Desktop Apps Mobile Apps & Web Databases Support & Setup QA & Test WordPress & CMS Other How it Works Become a Codementor Sign Up Sign In × {{alert.msg}} Never ask again Online Python Course: Learn Python in 4 Weeks View Class Tutorials / Python Writing and Using Custom Exceptions in Python #Python #Exception –{{showDate(postTime)}} This tutorial will go through the “what” and “why” of exceptions in Python, and then walk you through the process of creating and using your own types of exceptions. And more importantly, when not to. Enjoy! ##What is an Exception? If you have been coding in Python for any length of time, no doubt you have seen a traceback. Just in case you have

 

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