extremely simple plugin system with discovery

beets/plugins.py

@@ -0,0 +1,73 @@
+# This file is part of beets.
+# Copyright 2010, Adrian Sampson.
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+# 
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+
+"""Support for beets plugins."""
+
+import logging
+import itertools
+
+# Global logger.
+log = logging.getLogger('beets')
+
+PLUGIN_NAMESPACE = 'beetsplug'
+DEFAULT_PLUGINS = []
+
+class BeetsPlugin(object):
+    """The base class for all beets plugins. Plugins provide
+    functionality by defining a subclass of BeetsPlugin and overriding
+    the abstract methods defined here.
+    """
+    def commands(self):
+        """Should return a list of beets.ui.Subcommand objects for
+        commands that should be added to beets' CLI.
+        """
+        raise NotImplementedError
+
+def load_plugins(names=()):
+    """Imports the modules for a sequence of plugin names. Each name
+    must be the name of a Python module under the "beetsplug" namespace
+    package in sys.path; the module indicated should contain the
+    BeetsPlugin subclasses desired. A default set of plugins is also
+    loaded.
+    """
+    for name in itertools.chain(names, DEFAULT_PLUGINS):
+        modname = '%s.%s' % (PLUGIN_NAMESPACE, name)
+        try:
+            __import__(modname, None, None)
+        except:
+            log.warn('plugin %s not found' % name)
+
+_instances = {}
+def find_plugins():
+    """Returns a list of BeetsPlugin subclass instances from all
+    currently loaded beets plugins. Loads the default plugin set
+    first.
+    """
+    load_plugins()
+    plugins = []
+    for cls in BeetsPlugin.__subclasses__():
+        # Only instantiate each plugin class once.
+        if cls not in _instances:
+            _instances[cls] = cls()
+        plugins.append(_instances[cls])
+    return plugins
+
+def commands():
+    """Returns a list of Subcommand objects from all loaded plugins.
+    """
+    out = []
+    for plugin in find_plugins():
+        out += plugin.commands()
+    return out
+

beets/ui/__init__.py

@@ -24,6 +24,7 @@ import textwrap
 import ConfigParser
 
 from beets import library
+from beets import plugins
 
 # Constants.
 CONFIG_FILE = os.path.expanduser('~/.beetsconfig')
@@ -340,7 +341,9 @@ def main():
     from beets.ui.commands import default_commands
     
     # Construct the root parser.
-    parser = SubcommandsOptionParser(subcommands=default_commands)
+    commands = list(default_commands)
+    commands += plugins.commands()
+    parser = SubcommandsOptionParser(subcommands=commands)
     parser.add_option('-l', '--library', dest='libpath',
                       help='library database file to use')
     parser.add_option('-d', '--directory', dest='directory',
@@ -378,3 +381,4 @@ def main():
     except UserError, exc:
         message = exc.args[0] if exc.args else None
         subcommand.parser.error(message)
+

beets/ui/commands.py

@@ -505,3 +505,4 @@ def stats_func(lib, config, opts, args):
     show_stats(lib, ui.make_query(args))
 stats_cmd.func = stats_func
 default_commands.append(stats_cmd)
+

setup.py

@@ -22,7 +22,7 @@ def _read(fn):
     return open(path).read()
 
 setup(name='beets',
-      version='1.0b2',
+      version='1.0b3',
       description='music tagger and library organizer',
       author='Adrian Sampson',
       author_email='adrian@radbox.org',
@@ -37,7 +37,9 @@ setup(name='beets',
           'beets.ui',
           'beets.autotag',
           'beets.player',
+          'beetsplug',
       ],
+      namespace_packages=['beetsplug'],
       scripts=['beet'],
 
       install_requires=[