Introduced __plugin_init__ method called after all plugins have been discovered

Plugins may be able to use this method for final setups before the implementations and hooks are evaluated, e.g. for adjusting their offered functionality based on what other plugins are available.

src/octoprint/plugin/core.py

@@ -28,6 +28,8 @@ class PluginInfo(object):
 
 	attr_check = '__plugin_check__'
 
+	attr_init = '__plugin_init__'
+
 	def __init__(self, key, location, instance, version=None):
 		self.key = key
 		self.location = location
@@ -82,6 +84,10 @@ class PluginInfo(object):
 	def check(self):
 		return self._get_instance_attribute(self.__class__.attr_check, default=lambda: True)
 
+	@property
+	def init(self):
+		return self._get_instance_attribute(self.__class__.attr_init, default=lambda: True)
+
 	def _get_instance_attribute(self, attr, default=None):
 		if not hasattr(self.instance, attr):
 			return default
@@ -205,8 +211,14 @@ class PluginManager(object):
 		self.plugins = self._find_plugins()
 
 		for name, plugin in self.plugins.items():
+			# initialize the plugin
+			plugin.init()
+
+			# evaluate registered hooks
 			for hook, callback in plugin.hooks.items():
 				self.plugin_hooks[hook].append((name, callback))
+
+			# evaluate registered implementations
 			for plugin_type in self.plugin_types:
 				implementations = plugin.get_implementations(plugin_type)
 				self.plugin_implementations[plugin_type] += ( (name, implementation) for implementation in implementations )
@@ -240,13 +252,13 @@ class PluginManager(object):
 			return set()
 		return {impl[0]: impl[1] for impl in result}
 
-	def get_helpers(self, name, helpers=None):
+	def get_helpers(self, name, *helpers):
 		if not name in self.plugins:
 			return None
 		plugin = self.plugins[name]
 
 		all_helpers = plugin.helpers
-		if helpers:
+		if len(helpers):
 			return dict((k, v) for (k, v) in all_helpers.items() if k in helpers)
 		else:
 			return all_helpers