Questions re subclassing at "load time"
John J. Lee
jjl at pobox.com
Sun Jun 22 21:29:51 CEST 2003
"Edward K. Ream" <edreamleo at charter.net> writes:
> There appears to be an easy way for plugins to override classes in
> an app.
[...rebinding module-global names to new plugin classes...]
IIUC, you've discovered a variation of a nice Python pattern, in which
a class is not directly instantiated, but referred to through an
attribute of another class:
helper_class = Helper
self._helper = self.helper_class()
helper_class = NewHelper
spam = Foo()
eggs = NewFoo()
ham = Foo()
ham.helper_class = NewHelper
> Initial experiments appear to show that this scheme works well. My
> 1. Is this scheme completely safe? Anything to watch out for?
No tricky *technical* details that I'm aware of...
> 2. Any suggestions, improvements or simplifications?
...but, though I think fundamentally your idea is good, rebinding
module names seems at the least an unconventional way to implement it,
likely to lead to confusion in people reading your code. I don't see
any gain from that unconventional way of doing things (happy to be
proved wrong, though). Instead, why not use a class instance to
represent your application, and allow plugins to mess with that
(subject to certain rules, no doubt)? Or let the plugins define new
classes and register them.
Obviously, a major thing to consider is how you're going to stop one
plugin treading on the toes of another, to the extent that that's
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