Merge pull request #1 from sdelements/feature/graceful_failure

Make plugins fail gracefully

Author: emintham

yantra/manager.py

@@ -24,8 +24,19 @@ class PluginContainer(object):
 
     def __init__(self, plugin_type):
         self._plugins = []
+        self._errors = {}
         self.plugin_type = plugin_type
 
+    @property
+    def errors(self):
+        # clear errors from the last time we called get_plugins
+        self._errors = {}
+
+        # attempt to load the plugins and populate errors
+        self.get_plugins()
+
+        return self._errors
+
     def register_plugin(self, plugin_cls):
         """Register instance of the plugin class"""
         self._plugins.append(plugin_cls())
@@ -47,8 +58,8 @@ def _get_modules(self):
                     modname, ext = os.path.splitext(filename)
 
                     if ext == ".py":
-                        filename, path, desc = imp.find_module(modname, [directory_path])
-                        plugin_modules.append((modname, filename, path, desc,))
+                        fp, path, desc = imp.find_module(modname, [directory_path])
+                        plugin_modules.append((modname, fp, path, desc,))
 
         return plugin_modules
 
@@ -63,24 +74,29 @@ def get_plugins(self):
         self._plugins = []
 
         for plugin_module in modules:
-            modname, filename, path, desc = plugin_module
+            modname, fp, path, desc = plugin_module
 
-            if filename:
+            try:
                 # load the module and look for classes
-                module = imp.load_module(modname, filename, path, desc)
-                classes_in_module = inspect.getmembers(module, inspect.isclass)
+                module = imp.load_module(modname, fp, path, desc)
+            except Exception as e:
+                error_msg = e.__class__.__name__ + ': ' + e.message
+                self._errors[fp.name] = error_msg
+                continue
+
+            classes_in_module = inspect.getmembers(module, inspect.isclass)
 
-                for cls in classes_in_module:
-                    cls = cls[1]
+            for cls in classes_in_module:
+                cls = cls[1]
 
-                    # ignore if it's the base plugin class
-                    if cls.__name__ == self.plugin_type.base_class.__name__:
-                        continue
+                # ignore if it's the base plugin class
+                if cls.__name__ == self.plugin_type.base_class.__name__:
+                    continue
 
-                    # make sure that the class is a subclass of the plugin's
-                    # base class
-                    if self.plugin_type.base_class in cls.__bases__:
-                        self.register_plugin(cls)
+                # make sure that the class is a subclass of the plugin's
+                # base class
+                if self.plugin_type.base_class in cls.__bases__:
+                    self.register_plugin(cls)
 
         return self._plugins
 
@@ -97,6 +113,15 @@ def __init__(self, plugin_types=None):
         for plugin_type in plugin_types:
             self.register_plugin_type(plugin_type)
 
+    def _get_container(self, plugin_type):
+        try:
+            return self._containers[plugin_type.name]
+        except KeyError:
+            raise AssertionError("No plugins found for type: {0}: ".format(plugin_type))
+
+    def get_errors(self, plugin_type):
+        return self._get_container(plugin_type).errors
+
     def register_plugin_type(self, plugin_type):
         assert isinstance(plugin_type, PluginType)
 
@@ -106,12 +131,7 @@ def register_plugin_type(self, plugin_type):
         self._containers[plugin_type.name] = PluginContainer(plugin_type)
 
     def get_plugins(self, plugin_type):
-        try:
-            container = self._containers[plugin_type.name]
-        except KeyError:
-            raise AssertionError("No plugins found for type: {0}: ".format(plugin_type))
-
-        return container.get_plugins()
+        return self._get_container(plugin_type).get_plugins()
 
     def has_plugins(self, plugin_type):
         return bool(self.get_plugins(plugin_type))