From d1d7e4718d0c4323ff2923f209420ad77ba5410f Mon Sep 17 00:00:00 2001
From: Harvey Devereux <h.devereux@qmul.ac.uk>
Date: Fri, 8 Nov 2024 15:31:51 +0000
Subject: [PATCH] Check atoms is Atoms, clearer exception

---
 janus_core/processing/observables.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/janus_core/processing/observables.py b/janus_core/processing/observables.py
index 00b1de97..2d8d9083 100644
--- a/janus_core/processing/observables.py
+++ b/janus_core/processing/observables.py
@@ -180,7 +180,14 @@ def __call__(self, atoms: Atoms) -> list[float]:
         -------
         list[float]
             The stress components in GPa units.
+
+        Raises
+        ------
+        ValueError
+            If atoms is not an Atoms object.
         """
+        if not isinstance(atoms, Atoms):
+            raise ValueError("atoms should be an Atoms object")
         sliced_atoms = atoms[self.atoms_slice]
         # must be re-attached after slicing for get_stress
         sliced_atoms.calc = atoms.calc