Custom Error Class Python
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Python Custom Error Handler
each other. Join them; it only takes a minute: Sign up Proper way to declare custom exceptions in modern Python? up vote 581 down vote favorite 158 What's the proper way to declare custom exception classes in modern
Python Raise Custom Error
Python? My primary goal is to follow whatever standard other exception classes have, so that (for instance) any extra string I include in the exception is printed out by whatever tool caught the exception. By "modern Python" I mean something that will run in Python 2.5 but be 'correct' for the Python 2.6 and Python 3.* way of doing things. And by "custom" I mean an Exception object that can include extra data about the cause of python error class has no attribute the error: a string, maybe also some other arbitrary object relevant to the exception. I was tripped up by the following deprecation warning in Python 2.6.2: >>> class MyError(Exception): ... def __init__(self, message): ... self.message = message ... >>> MyError("foo") _sandbox.py:3: DeprecationWarning: BaseException.message has been deprecated as of Python 2.6 It seems crazy that BaseException has a special meaning for attributes named message. I gather from PEP-352 that attribute did have a special meaning in 2.5 they're trying to deprecate away, so I guess that name (and that one alone) is now forbidden? Ugh. I'm also fuzzily aware that Exception has some magic parameter args, but I've never known how to use it. Nor am I sure it's the right way to do things going forward; a lot of the discussion I found online suggested they were trying to do away with args in Python 3. Update: two answers have suggested overriding __init__, and __str__/__unicode__/__repr__. That seems like a lot of typing, is it necessary? python exception share|improve this question edited Jun 5 '12 at 20:37 Eitan T 27.8k113978 asked Aug 23 '09 at 21:29 Nelson 6,32032027 2 *args (or *foo, or *whatever, all that matters is that it has the star in front) is for functions that have an indefinite number of positional arguments. So if you have def myfunction(*args), you can call it like myfunction
you have probably seen some. There are (at least) two distinguishable kinds of errors: syntax errors and exceptions. 8.1. Syntax Errors¶ Syntax
Python Overflowerror
errors, also known as parsing errors, are perhaps the most common kind python try catch all of complaint you get while you are still learning Python: >>> while True print('Hello world') File "
output an error when something in it goes wrong. http://www.programiz.com/python-programming/user-defined-exception data-ad-client="ca-pub-9007421361448641" data-ad-slot="8057468026" However, sometimes you may need to create custom exceptions that serves 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 custom error are also derived form this class. >>> class CustomError(Exception): ... pass ... >>> raise CustomError Traceback (most recent call last): ... __main__.CustomError >>> raise CustomError("An error occurred") Traceback (most recent call last): ... __main__.CustomError: An error occurred Here, we have created a user-defined exception called CustomError which is python custom error derived from the Exception class. This new exception can be raised, like other exceptions, using the raise statement with an optional error message. When we are developing a large Python program, it is a good practice to place all the user-defined exceptions that our program raises in a separate file. Many standard modules do this. They define their exceptions separately as exceptions.py or errors.py (generally but not always). User-defined exception class can implement everything a normal class can do, but we generally make them simple and concise. Most implementations declare a custom base class and derive others exception classes from this base class. This concept is made clearer in the following example. Example: User-Defined Exception in Python In this example, we will illustrate how user-defined exceptions can be used in a program to raise and cat