[Twisted-Python] twisted.plugin issues

[Phil Christensen]

On Jun 30, 2007, at 9:32 PM, Jean-Paul Calderone wrote:

> On Sat, 30 Jun 2007 20:27:19 -0400, Phil Christensen  
> <phil at bubblehouse.org> wrote:
>> Hello all,
>>
>> I'm trying to implement a plugin system in a project using the   
>> twisted plugin framework. I've read through the docs pretty   
>> thoroughly, but I can't seem to figure out what I'm doing wrong.
>>
>> Attached is a sample case that should illustrate the problem. The   
>> layout is as follows:
>>
>>     plugin_dir/
>>     plugin_dir/test/
>>     plugin_dir/test/plugins/
>>     plugin_dir/test/plugins/myplugin.py
>>     test/
>>     test/__init__.py
>>     test/plugins/
>>     test/plugins/__init__.py
>>     test/sample.py
>>     test_plugin.py
>>
>> First I created the test.plugins package, and included the  
>> following  in test/plugins/__init__.py:
>>
>>     import os, sys
>>
>>     __path__ = [os.path.abspath(os.path.join(x, 'test', 'plugins'))
>>                     for x in sys.path]
>>
>>     __all__ = []
>>
>> Then I created my interfaces in the test.sample module:
>>
>>     from zope import interface
>>
>>     class ISamplePlugin(interface.Interface):
>>         '''My Sample Plugin Class'''
>>
>> Next, I created the plugin in an arbitrary directory, under  
>> plugin_dir/test/plugins/myplugin.py:
>>
>>     from zope.interface import implements
>>     from twisted import plugin
>>     from test.sample import ISamplePlugin
>>
>>     class MyPlugin(object):
>>         implements(plugin.IPlugin, ISamplePlugin)
>
> The problem may be here.  What happens if you use classProvides  
> instead of
> implements or bind an instance of MyPlugin to an attribute of this  
> module?

Aha, this looks promising. Doing either of those things results in:


Traceback (most recent call last):
   File "test_plugin.py", line 11, in ?
     for plugin in plugin_result:
   File "/Users/phil/Workspace/Twisted/twisted/plugin.py", line 186,  
in getPlugins
     allDropins = getCache(package)
--- <exception caught here> ---
   File "/Users/phil/Workspace/Twisted/twisted/plugin.py", line 165,  
in getCache
     dropinPath.setContent(pickle.dumps(dropinDotCache))
cPickle.PicklingError: Can't pickle <InterfaceClass  
test.sample.ISamplePlugin>: import of module test.sample failed
<class 'test.plugins.myplugin.MyPlugin'> was found.


So this must be pretty close. I tried deleting the dropin.cache, but  
I'm still getting this exception.


>>
>> Finally, here's the sample script that tries to load the plugins  
>> in  the arbitrary directory:
>>
>>     from twisted import plugin
>>
>>     import sys
>>     sys.path.append('.')
>>     sys.path.append('./plugin_dir')
>>
>>     from test import sample, plugins
>>     from twisted import plugin
>>     plugin_result = plugin.getPlugins(sample.ISamplePlugin, plugins)
>>
>>     for plugin in plugin_result:
>>         print repr(plugin) + ' was found.'
>>