ValueError that is thrown by _check_param_grid method now includes parameters name when values of a parameter have incorrect type.

Old ValueError:
ValueError: Parameter values should be a list.

New ValueError:
ValueError: Parameter(key1) values should be a non-empty list.

Author: b0noI

sklearn/grid_search.py

@@ -326,17 +326,18 @@ def _check_param_grid(param_grid):
         param_grid = [param_grid]
 
     for p in param_grid:
-        for v in p.values():
+        for name, v in p.items():
             if isinstance(v, np.ndarray) and v.ndim > 1:
                 raise ValueError("Parameter array should be one-dimensional.")
 
             check = [isinstance(v, k) for k in (list, tuple, np.ndarray)]
             if True not in check:
-                raise ValueError("Parameter values should be a list.")
+                raise ValueError("Parameter({0}) values should be a list."
+                                 "".format(name))
 
             if len(v) == 0:
-                raise ValueError("Parameter values should be a non-empty "
-                                 "list.")
+                raise ValueError("Parameter({0}) values should be a non-empty "
+                                 "list.".format(name))
 
 
 class _CVScoreTuple (namedtuple('_CVScoreTuple',