handling of errors

pyat/at/latticetools/observablelist.py

@@ -26,7 +26,7 @@
     "ObservableList",
 ]
 
-from collections.abc import Iterable
+from collections.abc import Iterable, Iterator
 from functools import reduce
 from typing import Callable
 
@@ -44,6 +44,17 @@ def _flatten(vals, order="F"):
     return np.concatenate([np.reshape(v, -1, order=order) for v in vals])
 
 
+class _ObsResIter(Iterator):
+    def __init__(self, obsiter):
+        self.base = obsiter
+
+    def __next__(self):
+        val = next(self.base)
+        if isinstance(val, Exception):
+            raise val
+        return val
+
+
 class _ObsResults(tuple):
     def __getitem__(self, item):
         if isinstance(item, slice):
@@ -54,6 +65,9 @@ def __getitem__(self, item):
                 raise AtError(f"Evaluation failed: {val.args[0]}") from val
             return val
 
+    def __iter__(self):
+        return _ObsResIter(super().__iter__())
+
 
 class ObservableList(list):
     """Handles a list of Observables to be evaluated together.
@@ -265,7 +279,7 @@ def obseval(ring, obs):
             """Evaluate a single observable."""
 
             def check_error(data, refpts):
-                return data if isinstance(data, AtError) else data[refpts]
+                return data if isinstance(data, Exception) else data[refpts]
 
             obsneeds = obs.needs
             obsrefs = getattr(obs, "_boolrefs", None)
@@ -385,7 +399,7 @@ def ringeval(
         trajs, orbits, rgdata, eldata, emdata, mxdata, geodata = ringeval(
             ring, dp=dp, dct=dct, df=df
         )
-        return [obseval(ring, ob) for ob in self]
+        return _ObsResults(obseval(ring, ob) for ob in self)
 
     def check(self) -> bool:
         """Check the evaluation

pyat/at/latticetools/observables.py

@@ -330,9 +330,12 @@ def evaluate(self, *data, initial: bool = False):
         """
         for d in data:
             if isinstance(d, Exception):
-                self._value = d
+                errtype = type(d)
+                err = errtype(f"Evaluation of {self.name} failed: {d.args[0]}")
+                err.__cause__ = d
+                self._value = err
                 self._shape = None
-                return d
+                return err
 
         val = np.asarray(self.fun(*data, *self.args, **self.kwargs))
         if initial:
@@ -357,7 +360,7 @@ def value(self):
         """Value of the observable."""
         val = self._value
         if isinstance(val, Exception):
-            raise AtError(f"Evaluation of {self.name} failed: {val.args[0]}") from val
+            raise val
         return val
 
     @property