fix(SingleTask): pull tag from input_tags, when not explicitly config…

…ured

Fixes bug introduced in bbbc6b4. Input
tags stopped being referenced when setting the tag on the output.

Needed to tag delayspectrum files properly in the daily pipeline.

draco/core/task.py

@@ -466,8 +466,15 @@ def _nan_process_output(self, output):
     def _interpolation_dict(self, output):
         # Get the set of variables the can be interpolated into the various strings
         idict = dict(output.attrs)
+        if "tag" in output.attrs:
+            tag = output.attrs["tag"]
+        elif "input_tags" in output.attrs and len(output.attrs["input_tags"]):
+            tag = output.attrs["input_tags"][0]
+        else:
+            tag = self._count
+
         idict.update(
-            tag=(output.attrs["tag"] if "tag" in output.attrs else self._count),
+            tag=tag,
             count=self._count,
             task=self.__class__.__name__,
             key=(