Fixes issue #392 (#589)

* added methods to the api

* tests

* update doc

* fix warning

* update tests

* minor

* fix comments

Author: ahmed-irfan

doc/sphinx/source/api-types.rst

@@ -1127,7 +1127,6 @@ Error Reports
 
       Model generalization failed for some other reason.
 
-
    .. c:enum:: YVAL_INVALID_OP
  
       Invalid operation on a value descriptor (node in the model DAG).