From e930baf2b4856b63d46536f17f6a600e0817baf1 Mon Sep 17 00:00:00 2001
From: jan <jan@mpxd.net>
Date: Tue, 5 Sep 2017 11:07:32 -0700
Subject: [PATCH] fix and improve error-checking for shifts parameter

---
 gridlock/grid.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/gridlock/grid.py b/gridlock/grid.py
index 817a229..e4787cb 100644
--- a/gridlock/grid.py
+++ b/gridlock/grid.py
@@ -307,9 +307,12 @@ class Grid(object):
         self.periodic = periodic
 
         self.shifts = numpy.array(shifts, dtype=float)
+        if len(self.shifts.shape) != 2:
+            raise GridError('Misshapen shifts: shifts must have two axes! '
+                            ' The given shifts has shape {}'.format(self.shifts.shape))
         if self.shifts.shape[1] != 3:
-            GridError('Misshapen shifts; second axis size should be 3,'
-                      ' shape is {}'.format(self.shifts.shape))
+            raise GridError('Misshapen shifts; second axis size should be 3,'
+                            ' shape is {}'.format(self.shifts.shape))
 
         num_shifts = self.shifts.shape[0]
         if num_grids is None: