Improve flexibility of the loader

homeassistant/loader.py

@@ -3,7 +3,17 @@ homeassistant.loader
 ~~~~~~~~~~~~~~~~~~~~
 
 Provides methods for loading Home Assistant components.
+
+This module has quite some complex parts. I have tried to add as much
+documentation as possible to keep it understandable.
+
+Components are loaded by calling get_component('switch') from your code.
+If you want to retrieve a platform that is part of a component, you should
+call get_component('switch.your_platform'). In both cases the config directory
+is checked to see if it contains a user provided version. If not available it
+will check the built-in components and platforms.
 """
+import os
 import sys
 import pkgutil
 import importlib
@@ -30,22 +40,27 @@ def prepare(hass):
         pkgutil.iter_modules(components.__path__, 'homeassistant.components.'))
 
     # Look for available custom components
+    custom_path = hass.get_config_path("custom_components")
 
-    # Ensure we can load custom components from the config dir
-    sys.path.append(hass.config_dir)
+    if os.path.isdir(custom_path):
+        # Ensure we can load custom components using Pythons import
+        sys.path.insert(0, hass.config_dir)
 
-    try:
-        # pylint: disable=import-error
-        import custom_components
+        # We cannot use the same approach as for built-in components because
+        # custom components might only contain a platform for a component.
+        # ie custom_components/switch/some_platform.py. Using pkgutil would
+        # not give us the switch component (and neither should it).
 
-        AVAILABLE_COMPONENTS.extend(
-            item[1] for item in
-            pkgutil.iter_modules(
-                custom_components.__path__, 'custom_components.'))
+        # Assumption: the custom_components dir only contains directories or
+        # python components. If this assumption is not true, HA won't break,
+        # just might output more errors.
+        for fil in os.listdir(custom_path):
+            if os.path.isdir(os.path.join(custom_path, fil)):
+                AVAILABLE_COMPONENTS.append('custom_components.{}'.format(fil))
 
-    except ImportError:
-        # No folder custom_components exist in the config directory
-        pass
+            else:
+                AVAILABLE_COMPONENTS.append(
+                    'custom_components.{}'.format(fil[0:-3]))
 
 
 def get_component(comp_name):
@@ -61,8 +76,10 @@ def get_component(comp_name):
     # an exception because it will try to import the parent.
     # Because of this behavior, we will approach loading sub components
     # with caution: only load it if we can verify that the parent exists.
+    # We do not want to silent the ImportErrors as they provide valuable
+    # information to track down when debugging Home Assistant.
 
-    # First check config dir, then built-in
+    # First check custom, then built-in
     potential_paths = ['custom_components.{}'.format(comp_name),
                        'homeassistant.components.{}'.format(comp_name)]
 
@@ -76,17 +93,30 @@ def get_component(comp_name):
             continue
 
         try:
-            _COMPONENT_CACHE[comp_name] = importlib.import_module(path)
+            module = importlib.import_module(path)
+
+            # In Python 3 you can import files from directories that do not
+            # contain the file __init__.py. A directory is a valid module if
+            # it contains a file with the .py extension. In this case Python
+            # will succeed in importing the directory as a module and call it
+            # a namespace. We do not care about namespaces.
+            # This prevents that when only
+            # custom_components/switch/some_platform.py exists,
+            # the import custom_components.switch would succeeed.
+            if module.__spec__.origin == 'namespace':
+                continue
 
             _LOGGER.info("Loaded %s from %s", comp_name, path)
 
-            return _COMPONENT_CACHE[comp_name]
+            _COMPONENT_CACHE[comp_name] = module
+
+            return module
+
         except ImportError:
             _LOGGER.exception(
                 ("Error loading %s. Make sure all "
                  "dependencies are installed"), path)
 
-    # We did find components but were unable to load them
-    _LOGGER.error("Unable to load component %s", comp_name)
+    _LOGGER.error("Unable to find component %s", comp_name)
 
     return None