raise est utilisé pour lever une exception qui pourrait se produire. Exemple : assert : la lecture d'un fichier de configuration lors du lancement d'une application ne doit pas poser problème. Tu peux utiliser une exception et traiter cela au démarrage, ou tu peux utiliser les assert.
raise without any arguments is a special use of python syntax. It means get the exception and re-raise it. If this usage it could have been called reraise. raise From The Python Language Reference: If no expressions are present, raise re-raises the last exception that was active in the current scope.
Raise exception (args) from original_exception. This statement is used to create exception chaining in which an exception that is raised in response to another exception can contain the details of the original exception - as shown in the example below. class MyCustomException(Exception): pass. a = 10.
With modern Python Exceptions, you don't need to abuse .message, or override .__str__() or .__repr__() or any of it. If all you want is an informative message when your exception is raised, do this: class MyException(Exception): pass raise MyException("My hovercraft is full of eels")
The from clause is used for exception chaining: if given, the second expression must be another exception class or instance, which will then be attached to the raised exception as the __cause__ attribute (which is writable). If the raised exception is not handled, both exceptions will be printed: >>> try:
try: assert False raise Exception('Python assertions are not working. This tool relies on Python assertions to do its job. Possible causes are running with the"-O" flag or running a precompiled (".pyo" or".pyc") module.') except AssertionError: pass
Most libraries and the python built-ins will raise and Exception of one type or another if something goes wrong. Often in you own code you will also want to raise an exception when you detect something going wrong. Let's say as an example you were writing an email address validator and you wanted to raise an exception if the address didn't contain an @ sign. you could have something like (This ...
By default, unlike an exception, a warning doesn't interrupt. After import warnings, it is possible to specify a Warnings class when generating a warning. If one is not specified, it is literally UserWarning by default. >>> warnings.warn('This is a default warning.') <string>:1: UserWarning: This is a default warning.
@John Machin: Don't think I can be held accountable for not honoring requests in comments of deleted answers I didn't and can't see.
Your attempt means"if bool, return value, else return the result of raise expression" - which is nonsense of course, because raise exception is itself a statement not an expression. There's no way to do this inline, and you shouldn't want to. Do it explicitly: if not bool: raise MyException return value