Hi All,
Has anyone ever written a plugin that depends on another plugin? If
so, where did you define the Interface?
I apologize if I'm missing something obvious, but I can't seem to
figure out the best way to do this, nor find any documentation or
tickets talking about it, fixes in the works, or examples of prior
art. TracDev/ComponentArchitecture talks about components extending
other components, but it doesn't look cleanly doable if those
components are both plugins. I hope I'm wrong; the rest of the
component architecture is so well thought out, it seems suprising that
this would have fallen through the cracks.
Here's the problem: If fooplugin calls ExtensionPoint(IBar), and
barplugin implements(IBar), then we have to have a sensible place to
define 'class IBar'. I haven't yet found a sensible place:
- We can define 'class IBar' in barplugin, but that means that
fooplugin has to import IBar from barplugin. This means that
barplugin has to be installed anywhere fooplugin is installed, which
means that when bazplugin gets invented and deprecates barplugin,
barplugin will still have to be installed anyway, because fooplugin
can't load without it. Here's an illustration:
__________foo.py__________
from bar import IBar
class Foo(Component):
bars = ExtensionPoint(IBar)
__________bar.py__________
class IBar(Interface):
...
class Bar(Component):
implements(IBar)
__________baz.py__________
# created later... replaces Bar, but we can't remove Bar
# because foo.py depends on it
class Baz(Component):
bars = ExtensionPoint(IBar)
- We can define 'class IBar' in fooplugin, but now we have the same
problem in reverse: barplugin has to import IBar from fooplugin.
This means that fooplugin has to be installed anywhere barplugin is
installed, which means that when bazplugin gets invented and
deprecates fooplugin, fooplugin will still have to be installed
anyway, because barplugin can't load without it. Here's an
illustration:
__________foo.py__________
class IBar(Interface):
...
class Foo(Component):
bars = ExtensionPoint(IBar)
__________bar.py__________
from foo import IBar
class Bar(Component):
implements(IBar)
__________baz.py__________
# created later... replaces Foo, but we can't remove Foo
# because bar.py depends on it
class Baz(Component):
bars = ExtensionPoint(IBar)
- We might define 'class IBar' in some dummy plugin whose only purpose
in life is to provide the interface contract, but that just
seems wrong.
- We might do something clever with Python namespaces, but I haven't
got my mind wrapped around it yet.
This is all aside from the fact that I haven't been able to get the
above 'import' to work at all if these plugins are installed as eggs
in /var/trac/blah/plugins -- they have to be installed in e.g.
/usr/lib/python2.3/site-packages instead. I don't know enough yet to
know if that is another flaw or just operator error.
What the heck am I missing?
Steve
--
Stephen G. Traugott (KG6HDQ)
UNIX/Linux Infrastructure Architect, TerraLuna LLC
[EMAIL PROTECTED]
http://www.stevegt.com -- http://Infrastructures.Org
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