Fix bug where plugin load would pull in plugin imports

shepherd/plugin.py

@@ -1,8 +1,9 @@
 #!/usr/bin/env python3
 
-from contextlib import suppress
+import inspect
 from abc import ABC, abstractmethod
 import importlib
+import logging
 
 from types import SimpleNamespace
 from collections import namedtuple
@@ -10,6 +11,7 @@ import sys
 import os
 
 import shepherd.scheduler
+log = logging.getLogger(__name__)
 
 
 class PluginLoadError(Exception):
@@ -259,12 +261,19 @@ def find_plugins(plugin_names, plugin_dir=None):
                 raise PluginLoadError("Could not find plugin "+plugin_name)
 
         # Scan imported module for Plugin subclass
-        attrs = [getattr(mod, name) for name in dir(mod)]
-        for attr in attrs:
-            with suppress(TypeError):
-                if issubclass(attr, Plugin):
-                    plugin_classes[plugin_name] = attr
-                    break
+        def is_module_plugin(member, module=mod):
+            return (inspect.isclass(member) and member.__module__ ==
+                    module.__name__ and issubclass(member, Plugin))
+
+        class_list = inspect.getmembers(mod, is_module_plugin)
+
+        if class_list:
+            if len(class_list) > 1:
+                log.warning(
+                    F"Plugin module {mod.__name__} has more than one shepherd.Plugin subclass.")
+            _, plugin_classes[plugin_name] = class_list[0]
+            log.info(F"Loading plugin {plugin_classes[plugin_name].__name__}"
+                     " from module {mod.__name__}")
         else:
             raise PluginLoadError("Imported shepherd plugin modules must contain a"
                                   " subclass of shepherd.plugin.Plugin, such as"