Development environment: First look for resources in the location pointed to by CALIBRE_DEVELOP_FROM. If not found, use the normal resource location

src/calibre/gui2/tag_view.py

@@ -215,7 +215,7 @@ class TagsModel(QAbstractItemModel):
             return QModelIndex()
 
         child_item = index.internalPointer()
-        parent_item = child_item.parent
+        parent_item = getattr(child_item, 'parent', None)
 
         if parent_item is self.root_item or parent_item is None:
             return QModelIndex()

src/calibre/utils/resources.py

@@ -9,9 +9,22 @@ __docformat__ = 'restructuredtext en'
 
 import __builtin__, sys, os
 
+_dev_path = os.environ.get('CALIBRE_DEVELOP_FROM', None)
+if _dev_path is not None:
+    _dev_path = os.path.join(os.path.abspath(os.path.dirname(_dev_path)), 'resources')
+    if not os.path.exists(_dev_path):
+        _dev_path = None
+
 def get_path(path, data=False):
+    global _dev_path
     path = path.replace(os.sep, '/')
-    path = os.path.join(sys.resources_location, *path.split('/'))
+    base = None
+    if _dev_path is not None:
+        if os.path.exists(os.path.join(_dev_path, *path.split('/'))):
+            base = _dev_path
+    if base is None:
+        base = sys.resources_location
+    path = os.path.join(base, *path.split('/'))
     if data:
         return open(path, 'rb').read()
     return path