move event-handling logic into plugin system

beets/events.py

@@ -1,56 +0,0 @@
-# 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.
-
-#All the handlers for the event system.
-#Each key of the dictionary should contain a list of functions to be called
-#for any event. Functions will be called in the order they were added.
-handlers = { }
-
-def addEventListener(event, function):
-    """Adds an event listener to call function() when the specified event
-    (as a string) happens. The parameters passed to function will vary
-    depending on what event occured.
-
-    The function should respond to named parameters. function(**kwargs) will
-    trap all arguments in a dictionary."""
-    global handlers
-    
-    if event not in handlers:
-        handlers[event] = [ ] #Empty list to store the handlers
-    handlers[event].append(function)
-
-def send(event, **arguments):
-    """Sends an event to all assigned event listeners. Event is the name of 
-    the event to send, all other named arguments go to the event handler(s).
-
-    Returns the number of handlers called."""
-
-    if event in handlers:
-        for handler in handlers[event]:
-            handler(**arguments)
-        return len(handlers[event])
-    else:
-        return 0
-
-def listen(event):
-    """Decorator method for creating an event listener.
-
-    @events.listen("imported")
-    def importListener(**kwargs):
-        pass"""
-    def helper(funct):
-        addEventListener(event, funct)
-        return funct
-
-    return helper

beets/plugins.py

@@ -17,12 +17,16 @@
 import logging
 import itertools
 import traceback
+from collections import defaultdict
+
+PLUGIN_NAMESPACE = 'beetsplug'
+DEFAULT_PLUGINS = ['bpd']
 
 # Global logger.
 log = logging.getLogger('beets')
 
-PLUGIN_NAMESPACE = 'beetsplug'
-DEFAULT_PLUGINS = ['bpd']
+
+# Managing the plugins themselves.
 
 class BeetsPlugin(object):
     """The base class for all beets plugins. Plugins provide
@@ -35,6 +39,28 @@ class BeetsPlugin(object):
         """
         raise NotImplementedError
 
+    listeners = None
+    @classmethod
+    def listen(cls, event):
+        """Decorator that adds a function as an event handler for the
+        specified event (as a string). The parameters passed to function
+        will vary depending on what event occurred.
+
+        The function should respond to named parameters.
+        function(**kwargs) will trap all arguments in a dictionary.
+        Example:
+
+            >>> @MyPlugin.listen("imported")
+            >>> def importListener(**kwargs):
+            >>>     pass
+        """
+        def helper(func):
+            if cls.listeners is None:
+                cls.listeners = defaultdict(list)
+            cls.listeners[event].append(func)
+            return func
+        return helper
+
 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
@@ -72,6 +98,9 @@ def find_plugins():
         plugins.append(_instances[cls])
     return plugins
 
+
+# Plugin commands.
+
 def commands():
     """Returns a list of Subcommand objects from all loaded plugins.
     """
@@ -80,3 +109,31 @@ def commands():
         out += plugin.commands()
     return out
 
+
+# Event dispatch.
+
+# All the handlers for the event system.
+# Each key of the dictionary should contain a list of functions to be
+# called for any event. Functions will be called in the order they were
+# added.
+_event_handlers = defaultdict(list)
+
+def load_listeners():
+    """Loads and registers event handlers from all loaded plugins.
+    """
+    for plugin in find_plugins():
+        if plugin.listeners:
+            for event, handlers in plugin.listeners.items():
+                _event_handlers[event] += handlers
+
+def send(event, **arguments):
+    """Sends an event to all assigned event listeners. Event is the
+    name of  the event to send, all other named arguments go to the
+    event handler(s).
+
+    Returns the number of handlers called.
+    """
+    handlers = _event_handlers[event]
+    for handler in handlers:
+        handler(**arguments)
+    return len(handlers)

beets/ui/__init__.py

@@ -406,7 +406,8 @@ def main():
     # Load requested plugins.
     plugnames = config_val(config, 'beets', 'plugins', '')
     plugins.load_plugins(plugnames.split())
-    events.send("pluginload")
+    plugins.load_listeners()
+    plugins.send("pluginload")
 
     # Construct the root parser.
     commands = list(default_commands)