Am 15.02.10 23:12, schrieb Florian Ludwig:
On Sun, 2010-02-14 at 18:47 +0100, Diez B. Roggisch wrote:
Here there problem with the trac (and other plugin systems I've
seen)
approach:
You need to define something like:
|
| class IAuthPlugin(Interface): [...]
|
in your blog software.
Why? Any reason you can't define it in a separate package the
blog-software depends on, as well as your wiki?
That's actually my point - most plugin systems I've seen, like the one
trac uses, are not encouraging you to do so. Having a module that just
defines an Interface is kind of weird - and in the real world no one is
doing it.
Just because nobody doesn't do it doesn't mean it's not desirable. IMHO
the ones using interfaces usually immediatly implement them for some
cases - so you actually get the interface for you authentication
framework, and also implement an OpenID plugin for it. And this forms
one package. Then you can add new packages that implement other things.
repoze.who and what are examples for such design.
And then of course, this is not really needed. In Python, behavior
counts, not type-information. So you can get away without any explicit
declared interface. You might chose to not do that, for aestetic
reasons, or better documentation. But you aren't forced.
Actually some plugin-systems in python do force you and they check if
your "implementation" comply with the "interface".
I didn't say nobody does it, I just said it isn't needed to get a
working plugin system. If you don't want to have a separate package
*and* don't want to pull in any unused code, this is pretty much your
only option.
Here is one solution I came up with. Based on the earlier example:
Lets say you program a wiki and like to allow different kind of
authentications. So you create two plugins (for example one for
OpenID and one for Shibboleth).
Some time later you feel like reinventing the wheel again and
you program a blog. Again you like to allow different ways of
authentication and you already wrote plugins for exactly the
same for your wiki, right?
auth_openid.py - providing the authentication service
http://dpaste.com/hold/159619/
wiki.py - providing the wiki
http://dpaste.com/hold/159634/
Now putting both together:
import pbus
import wiki
import auth_openid
# or: import auth_shibboleth
pbus.get("wiki").run()
No interface definitions.
What do you think? Any obvious pitfalls (besides reinventing something)?
I don't know what pbus is supposed to do. Nor how it's laid out on a
python package level.
Diez
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