added a verbose exception

theano/tensor/basic.py

@@ -5303,6 +5303,12 @@ class Dot(Op):
             z[0] = numpy.asarray(numpy.dot(x, y))
         except ValueError, e:
             # The error raised by numpy has no shape information, we mean to add that
+            if config.exception_verbosity == 'high':
+                raise ValueError('dot product failed.\n'
+                        'First arg dims: '+str(x.shape)+'\n'
+                        'Second arg dims: '+str(y.shape)+'\n'
+                        'First arg: \n'+min_informative_str(node.inputs[0])+'\n'
+                        'Second arg: \n'+min_informative_str(node.inputs[1]))
             e.args = e.args + (x.shape, y.shape)
             raise