add _model_to_exptype method to AbstractModelLibrary (#201)

changes/201.bugfix.rst

@@ -0,0 +1 @@
+Add hook to allow ModelLibrary subclasses to override exptype.

docs/source/model_library.rst

@@ -393,6 +393,7 @@ Several methods are abstract and will need implementations:
 It's likely that a few other methods might require overriding:
 
 - ``_model_to_filename``
+- ``_model_to_exptype``
 - ``_assign_member_to_model``
 
 Consult the docstrings (and base implementations) for more details.

src/stpipe/library.py

@@ -231,7 +231,7 @@ def __init__(
                 else:
                     model = model_or_filename
 
-                exptype = getattr(model.meta, "exptype", "SCIENCE")
+                exptype = self._model_to_exptype(model)
 
                 if asn_exptypes is not None and exptype.lower() not in asn_exptypes:
                     continue
@@ -612,8 +612,8 @@ def _save(self, path, **kwargs):
                 members.append(
                     {
                         "expname": str(mfn),
-                        "exptype": model.meta.exptype,
-                        "group_id": model.meta.group_id,
+                        "exptype": self._model_to_exptype(model),
+                        "group_id": self._model_to_group_id(model),
                     }
                 )
                 self.shelve(model, i, modify=False)
@@ -626,7 +626,7 @@ def _save(self, path, **kwargs):
     def get_crds_parameters(self):
         """
         Get the "crds_parameters" from either:
-            - the first "science" member (based on model.meta.exptype)
+            - the first "science" member (based on exptype)
             - the first model (if no "science" member is found)
 
         If no "science" members are found in the library a ``UserWarning``
@@ -781,6 +781,28 @@ def _to_group_id(self, model_or_filename, index):
         except NoGroupID:
             return f"exposure{index + 1:04d}"
 
+    def _model_to_exptype(self, model):
+        """
+        Compute "exptype" from a model using the DataModel interface.
+
+        This will be called for every model in the library:
+            - when the library is created from a list of models
+            - when _save is called
+        In both cases the models are all in memory and this method
+        can use the in memory DataModel to determine the "exptype"
+        (likely ``model.meta.exptype``).
+
+        Parameters
+        ----------
+        model : DataModel
+
+        Returns
+        -------
+        exptype : str
+            Exposure type (for example "SCIENCE").
+        """
+        return getattr(model.meta, "exptype", "SCIENCE")
+
     @property
     @abc.abstractmethod
     def crds_observatory(self):
@@ -851,10 +873,12 @@ def _model_to_group_id(self, model):
         """
         Compute a "group_id" from a model using the DataModel interface.
 
-        This will be called for every model in the library ONLY when
-        the library is created from a list of models. In this case the
-        models are all in memory and this method can use the in memory
-        DataModel to determine the "group_id" (likely `model.meta.group_id`).
+        This will be called for every model in the library:
+            - when the library is created from a list of models
+            - when _save is called
+        In both cases the models are all in memory and this method
+        can use the in memory DataModel to determine the "group_id"
+        (likely ``model.meta.group_id``).
 
         If no "group_id" can be determined `NoGroupID` should be
         raised (to allow the library to assign a unique "group_id").