EZCeption (and EZMessage)

These classes provide a simplified means to define exception classes and message attributes.

Goals

• Less boilerplate to define error classes so they'll be used more.
• Formatting does not happen at raise time so catching errors doesn't incur string computation cost.
• Exception fields are easier to probe by exception handlers.
• Class-bases exceptions are a snap to define.
• Works with regular Python exception classes.
• Interfaces with the gettext module by default.
• Allows for associating other i18n messaging in the error classes.

Installation.

pip install ezception

NOTE: ezception is not on pypi yet. Until official releases are available:

pip install https://github.com/hrharkins/ezception/archive/master.zip

Usage

import ezception

class MyWebRequester(object):

    class Error(ezception.EZCeption):
        'A general error has occurred.'

    class OpenError(Error):
        'An error opening {self.url!r} has occurred.'

    class NoURLError(OpenError):
        '''
        No URL was provided.
        ''''

    class NoURLError(OpenError):
        '''
        The scheme {self.scheme!r} is not acceptable.
        '''

    ...

    def open(self, url):
        ... stuff happens.

        ... Oh noes!
        raise self.BadSchemeError(scheme=url.scheme)

So in the example the class defines a simple hierarchy of errors. Progreammers can trivially trap MyWebRequester.Error to catch anything generated by MyWebRequester. Because it's very simple to define those errors, a more robust exception hierarchy is more likely to emerge.

In addition, the message is NOT generated at exception time. Because of this, it is easy to catch and determine better handling code. The default Python exceptions use args, which requires the programmer to have tighter coupling with the error classes to acquire the parameters of the failure (or the error class needs to define more properties).

Only when the exception is printed does stringification occur. In addition, the message to be presented is processed using the gettext module, so adding support for other languages for such messages is possible using regular .po files. All messages are tracked by a global ezception.ALL_MSGS dict so generating base .po files is also simplified.