Application Plugin Framework

[Kay Schluehr]

Ron wrote:
> Hello,
>
> I'm attempting to develop a  plugin framework for an application that I'm
> working on.  I wish to develop something in which all plugins exist in a
> directory tree.  The framework need only be given the root of the tree.  The
> framework then uses os.path.walk to search all for all files named
> 'plugin.pyc'.  These are then loaded using imp.load_compiled().  They need
> contain only one variable called 'plugin' which is a reference to an
> instance of the plugin object.  This is extrated from the loaded module
> using getattr.  After that, the plugins are easy to work with since they
> implement a standard interface.  Or so the theory goes.  And this does work
> fine provided the plugin is implemented entirely within that one file.  If
> there are support modules that the main plugin module imports, which exist
> in the plugin's directory, then I get problems.  The imports fail.  I get
> "ImportError:  No module named <support module name>"
>
> Here's PluginManager.py:
> ####################
>
> import os
>
>
> class PluginManager( object ):
>    def __init__( self, pluginDir ):
>       self._plugins = { }
>
>       os.path.walk( pluginDir, self._addPlugin, None )
>
>    def _addPlugin( self, arg, dirname, names ):
>       import imp
>
>       for filename in names:
>          fullFilename = os.path.join( dirname, filename )
>          if os.path.isfile( fullFilename ) and (filename == 'plugin.pyc'):
>             module = imp.load_compiled( 'plugin', fullFilename )
>             self._plugins[ plugin.name ] = getattr( module, 'plugin' )
>             return
>
> PM = PluginManager( r'C:\Personal\SWDev\ModuleTest' )     # Root of the
> plugin directory tree
>
> print 'Plugin List: ', PM._plugins.keys()
>
> for name,plugin in PM._plugins.iteritems():
>    plugin.doSomething( )
>
> print 'done!'
>
> #######################
> My plugin.py file is in C:\Personal\SWDev\ModuleTest\Plugins\MyPlugin.  It's
> called plugin.pyc (which I compiled from the following source by importing
> it into the interactive python shell.
> #######################
>
> import work
>
>
> class MyPlugin( object ):
>    def __init__( self ):
>       self.name  = 'MyPlugin'
>
>    def doSomething( self ):
>       work.foo( )
>
>
> plugin = MyPlugin( )
>
> #######################
> Finally, work.py is in the same directory as plugin.py
> #######################
>
> def foo( ):
>    print 'foo called'
>
> ######################

Hi Ron,

the import directive does not lookup work.py in the same directory as
plugin.py. It searches through the directory of PluginManager.py and
otherwise searches through the directories of sys.path. The solution is
referencing work.py relative to the dir of the PluginManager.
MyFramework/
                    __init__.py
                    PluginManager.py
                    Plugins/
                               plugin.py
                               work.py


#######################
plugin.py
#######################
import MyFramework.Plugins.work as work

# do some stuff...

If import still causes trouble add the path of MyFramework to sys.path.


Regards,
Kay