Current Path : /usr/share/pyshared/computerjanitor/ |
Current File : //usr/share/pyshared/computerjanitor/plugin.py |
# plugin.py - plugin base class for computerjanitor # Copyright (C) 2008 Canonical, Ltd. # # This program is free software: you can redistribute it and/or modify # it under the terms of the GNU General Public License as published by # the Free Software Foundation, version 3 of the License. # # This program is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU General Public License for more details. # # You should have received a copy of the GNU General Public License # along with this program. If not, see <http://www.gnu.org/licenses/>. import imp import inspect import logging import os import computerjanitor _ = computerjanitor.setup_gettext() class Plugin(object): """Base class for plugins. These plugins only do one thing: identify cruft. See the 'get_cruft' method for details. """ def get_condition(self): if hasattr(self, "_condition"): return self._condition else: return [] def set_condition(self, condition): self._condition = condition condition = property(get_condition, set_condition) def set_application(self, app): """Set the Application instance this plugin belongs to. This is used by the plugin manager when creating the plugin instance. In a perfect world, this would be done via the __init__ method, but since I took a wrong left turn, I ended up in an imperfect world, and therefore giving the Application instance to __init__ would mandate that all sub-classes would have to deal with that explicitly. That is a lot of unnecessary make-work, which we should avoid. Therefore, we do it via this method. The class may access the Application instance via the 'app' attribute. """ self.app = app def do_cleanup_cruft(self): # pragma: no cover """Find cruft and clean it up. This is a helper method. """ for cruft in self.get_cruft(): cruft.cleanup() self.post_cleanup() def get_cruft(self): """Find some cruft in the system. This method MUST return an iterator (see 'yield' statement). This interface design allows cruft to be collected piecemeal, which makes it easier to show progress in the user interface. The base class default implementation of this raises an exception. Subclasses MUST override this method. """ raise computerjanitor.UnimplementedMethod(self.get_cruft) def post_cleanup(self): """Does plugin wide cleanup after the individual cleanup was performed. This is useful for stuff that needs to be proccessed in batches (e.g. for performance reasons) like package removal. """ pass class PluginManager(object): """Class to find and load plugins. Plugins are stored in files named '*_plugin.py' in the list of directories given to the initializer. """ def __init__(self, app, plugin_dirs): self._app = app self._plugin_dirs = plugin_dirs self._plugins = None def get_plugin_files(self): """Return all filenames in which plugins may be stored.""" names = [] for dirname in self._plugin_dirs: if not os.path.exists(dirname): continue basenames = [x for x in os.listdir(dirname) if x.endswith("_plugin.py")] logging.debug("Plugin modules in %s: %s" % (dirname, " ".join(basenames))) names += [os.path.join(dirname, x) for x in basenames] return names def _find_plugins(self, module): """Find and instantiate all plugins in a module.""" plugins = [] for dummy, member in inspect.getmembers(module): if inspect.isclass(member) and issubclass(member, Plugin): plugins.append(member) logging.debug("Plugins in %s: %s" % (module, " ".join(str(x) for x in plugins))) return [plugin() for plugin in plugins] def _load_module(self, filename): """Load a module from a filename.""" logging.debug("Loading module %s" % filename) module_name, dummy = os.path.splitext(os.path.basename(filename)) f = file(filename, "r") try: module = imp.load_module(module_name, f, filename, (".py", "r", imp.PY_SOURCE)) except Exception, e: # pragma: no cover logging.warning("Failed to load plugin '%s' (%s)" % (module_name, e)) return None f.close() return module def get_plugins(self, condition=[], callback=None): """Return all plugins that have been found. If callback is specified, it is called after each plugin has been found, with the following arguments: filename, index of filename in list of files to be examined (starting with 0), and total number of files to be examined. The purpose of this is to allow the callback to inform the user in case things take a long time. """ if self._plugins is None: self._plugins = [] filenames = self.get_plugin_files() for i in range(len(filenames)): if callback: callback(filenames[i], i, len(filenames)) module = self._load_module(filenames[i]) for plugin in self._find_plugins(module): plugin.set_application(self._app) self._plugins.append(plugin) # get the matching plugins plugins = [p for p in self._plugins if (p.condition == condition) or (condition in p.condition) or (condition == "*") ] logging.debug("plugins for condition '%s' are '%s'" % (condition, plugins)) return plugins