Move PluginManager out of api folder

openedx/core/lib/plugins.py

@@ -0,0 +1,45 @@
+"""
+Adds support for first class features that can be added to the edX platform.
+"""
+
+from stevedore.extension import ExtensionManager
+
+
+class PluginError(Exception):
+    """
+    Base Exception for when an error was found regarding features.
+    """
+    pass
+
+
+class PluginManager(object):
+    """
+    Base class that manages plugins to the edX platform.
+    """
+    @classmethod
+    def get_available_plugins(cls):
+        """
+        Returns a dict of all the plugins that have been made available through the platform.
+        """
+        # Note: we're creating the extension manager lazily to ensure that the Python path
+        # has been correctly set up. Trying to create this statically will fail, unfortunately.
+        if not hasattr(cls, "_plugins"):
+            plugins = {}
+            extension_manager = ExtensionManager(namespace=cls.NAMESPACE)  # pylint: disable=no-member
+            for plugin_name in extension_manager.names():
+                plugins[plugin_name] = extension_manager[plugin_name].plugin
+            cls._plugins = plugins
+        return cls._plugins
+
+    @classmethod
+    def get_plugin(cls, name):
+        """
+        Returns the plugin with the given name.
+        """
+        plugins = cls.get_available_plugins()
+        if name not in plugins:
+            raise PluginError("No such plugin {name} for entry point {namespace}".format(
+                name=name,
+                namespace=cls.NAMESPACE  # pylint: disable=no-member
+            ))
+        return plugins[name]