_Filters is frozen

Author: amorison

src/stagpy/stagyydata.py

@@ -488,7 +488,7 @@ def _bind(self, isnap: int, istep: int) -> None:
         self.sdat.steps[istep]._isnap = isnap
 
 
-@dataclass
+@dataclass(frozen=True)
 class _Filters:
     """Filters on a step view."""