improved documentation for config.from_object (#1870)

docs/config.rst

@@ -310,6 +310,7 @@ that experience:
     limit yourself to request-only accesses to the configuration you can
     reconfigure the object later on as needed.
 
+.. _config-dev-prod:
 
 Development / Production
 ------------------------

flask/config.py

@@ -143,10 +143,12 @@ class Config(dict):
         -   a string: in this case the object with that name will be imported
         -   an actual object reference: that object is used directly
 
-        Objects are usually either modules or classes.
+        Objects are usually either modules or classes. :meth:`from_object`
+        loads only the uppercase attributes of the module/class. A ``dict``
+        object will not work with :meth:`from_object` because the keys of a
+        ``dict`` are not attributes of the ``dict`` class.
 
-        Just the uppercase variables in that object are stored in the config.
-        Example usage::
+        Example of module-based configuration::
 
             app.config.from_object('yourapplication.default_config')
             from yourapplication import default_config
@@ -157,6 +159,9 @@ class Config(dict):
         with :meth:`from_pyfile` and ideally from a location not within the
         package because the package might be installed system wide.
 
+        See :ref:`config-dev-prod` for an example of class-based configuration
+        using :meth:`from_object`.
+
         :param obj: an import name or object
         """
         if isinstance(obj, string_types):