Jean-Michel Pichavant schrieb:
Hi fellows,
Does anyone know a way to write virtual methods (in one virtual class)
that will raise an exception only if called without being overridden ?
Currently in the virtual method I'm checking that the class of the
instance calling the method has defined that method as well.
Example:
class Stream(object):
"""Interface of all stream objects"""
def resetStats(self):
"""Reset the stream statistics. All values a zeroed except the
date."""
_log.info('Reset statistics of %s' % self)
if self.__class__.resetStats == Stream.resetStats:
raise NotImplementedError()
It works but it's tedious, I have to add these 2 lines to every virtual
method, changing the content of the 2 lines.
Maybe there is a nice/builtin way to do so (python 2.4)
Python has no concept of "virtual" methods. A simple
class Stream(object):
def resetStats(self):
raise NotImplemented
is all you need. Once a subclass overrides resetStats, that
implementatino is used.
Additionally, there are modules such as zope.interface out there, that
let you define more formally what an interface is, and declare who's
implementing it. I don't used this myself though, so I can't really
comment to which extend it e.g. warns you if you subclass *without*
implementing.
Diez
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