Merge pull request #1201 from goodfeli/shorter_error

theano/tensor/basic.py

@@ -603,11 +603,33 @@ def get_scalar_constant_value(v):
 
             # This is needed when we take the grad as the Shape op
             # are not already changed into MakeVector
-            if (v.owner.inputs[0].owner and
-                isinstance(v.owner.inputs[0].owner.op,
+            owner = v.owner
+            leftmost_parent = owner.inputs[0]
+            if (leftmost_parent.owner and
+                isinstance(leftmost_parent.owner.op,
                            theano.tensor.Shape)):
-                if v.owner.inputs[0].owner.inputs[0].type.broadcastable[
-                    v.owner.op.idx_list[0]]:
+                op = owner.op
+                idx_list = op.idx_list
+                idx = idx_list[0]
+                grandparent = leftmost_parent.owner.inputs[0]
+                gp_broadcastable = grandparent.type.broadcastable
+                ndim = grandparent.type.ndim
+
+                assert ndim == len(gp_broadcastable)
+
+                if not (idx < len(gp_broadcastable)):
+                    msg = "get_scalar_constant_value detected " + \
+                            "deterministic IndexError: x.shape[%d] " + \
+                            "when x.ndim=%d." % (ndim, idx)
+                    if config.exception_verbosity == 'high':
+                        msg += 'x=%s' % min_informative_str(x)
+                    else:
+                        msg += 'x=%s' % str(x)
+                    raise ValueError(msg)
+
+
+
+                if gp_broadcastable[idx]:
                     return numpy.asarray(1)
 
     raise NotScalarConstantError(v)