Cleaning up pol_convention handling when already applied to UVData

Author: kartographer

src/pyuvdata/utils/uvcalibrate.py

@@ -61,8 +61,13 @@ def _get_pol_conventions(
                 f"different values: {uvd_pol_convention} and {uvdata.pol_convention}."
             )
     else:
-        if uvdata.pol_convention is not None:
-            raise ValueError("You are trying to calibrate already-calibrated data.")
+        if uvdata.pol_convention is not None and (
+            uvc_pol_convention != uvdata.pol_convention
+        ):
+            raise ValueError(
+                "UVData already has a pol_convention applied that does not match UVCal "
+                f"convention: {uvdata.pol_convention} and {uvc_pol_convention}."
+            )
         if uvd_pol_convention is None:
             uvd_pol_convention = uvc_pol_convention
 

src/pyuvdata/uvdata/mir.py

@@ -714,7 +714,7 @@ def _init_from_mir_parser(
         self.uvw_array = (-1.0) * uvw_array
 
         self.vis_units = "Jy"
-        # self.pol_convention = "avg"
+        self.pol_convention = "avg"
 
         isource = np.unique(mir_data.in_data["isource"])
         for sou_id in isource:

tests/utils/test_uvcalibrate.py

@@ -97,14 +97,14 @@ def test_uvd_uvdata_different(self):
 
     def test_calibrate_already_calibrated(self):
         with pytest.raises(
-            ValueError, match="You are trying to calibrate already-calibrated data"
+            ValueError, match="UVData already has a pol_convention applied"
         ):
             _get_pol_conventions(
-                uvdata=SimpleNamespace(pol_convention="avg"),
+                uvdata=SimpleNamespace(pol_convention="sum"),
                 uvcal=SimpleNamespace(pol_convention="avg"),
                 undo=False,
                 uvc_pol_convention="avg",
-                uvd_pol_convention="avg",
+                uvd_pol_convention="sum",
             )
 
     @pytest.mark.parametrize("which", ["uvc", "uvd"])