Check class type in equality check.

pes_to_spec/config.py

@@ -106,10 +106,12 @@ class VSConfig(object):
         diff.gas = set(self.gas).difference(set(other.gas))
         return diff
 
-    def __eq__(self, other: 'VSConfig') -> bool:
+    def __eq__(self, other: object) -> bool:
         """
         Check if two configurations match.
         """
+        if not isinstance(other, VSConfig):
+            raise ValueError("I can only check equality with another VSConfig object.")
         diff = self - other
         for k, v in diff.voltage.items():
             if np.fabs(v) > 0.1: