Merge pull request #2624 from keflavich/issue2560

Add blank table handling for new returns from heasarc

Author: bsipocz

CHANGES.rst

@@ -81,6 +81,11 @@ casda
 - Use the standard ``login`` method for authenticating, which supports the system
   keyring [#2386]
 
+heasarc
+^^^^^^^
+
+- Fix issue 2560 in which blank tables raised exceptions [#2624]
+
 ipac.nexsci.nasa_exoplanet_archive
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

astroquery/heasarc/core.py

@@ -233,6 +233,18 @@ def _fallback(self, text):
 
         return Table_read(data, hdu=1)
 
+    def _blank_table_fallback(self, data):
+        """
+        In late 2022, we started seeing examples where the null result came
+        back as a FITS file with an ImageHDU and no BinTableHDU.
+        """
+        with fits.open(data) as fh:
+            comments = fh[1].header['COMMENT']
+        emptytable = Table()
+        emptytable.meta['COMMENT'] = comments
+        warnings.warn(NoResultsWarning("No matching rows were found in the query."))
+        return emptytable
+
     def _parse_result(self, response, verbose=False):
         # if verbose is False then suppress any VOTable related warnings
         if not verbose:
@@ -250,6 +262,10 @@ def _parse_result(self, response, verbose=False):
             warnings.warn(NoResultsWarning("No matching rows were found in the query."))
             return Table()
 
+        if "XTENSION= 'IMAGE   '" in response.text:
+            data = BytesIO(response.content)
+            return self._blank_table_fallback(data)
+
         try:
             data = BytesIO(response.content)
             return Table_read(data, hdu=1)
@@ -259,6 +275,7 @@ def _parse_result(self, response, verbose=False):
             except Exception:
                 return self._old_w3query_fallback(response.content)
 
+
     def _args_to_payload(self, **kwargs):
         """
         Generates the payload based on user supplied arguments

astroquery/heasarc/tests/data/be6d5c35.dat

@@ -0,0 +1 @@
+SIMPLE  =                    T / Browse (FitsDisplay V0.2)                      BITPIX  =                    8                                                  NAXIS   =                    0 / Dummy HDU                                      EXTEND  =                    T / Extensions allowed                             END                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             XTENSION= 'IMAGE   '           / Tables not returning data                      BITPIX  =                    8                                                  NAXIS   =                    0                                                  PCOUNT  =                    0                                                  GCOUNT  =                    1                                                                                                                                  COMMENT    heasarc_fermilpsc : No matching rows                                 END                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             

astroquery/heasarc/tests/test_heasarc_remote.py

@@ -7,6 +7,11 @@
 
 from .conftest import MockResponse, parametrization_local_save_remote, skycoord_3C_273
 
+from astroquery.exceptions import NoResultsWarning
+
+from astropy.coordinates import SkyCoord
+from astropy import units as u
+
 
 @parametrization_local_save_remote
 class TestHeasarc:
@@ -96,3 +101,23 @@ def test_query_region(self):
             skycoord_3C_273, mission=mission, radius="1 degree")
 
         assert len(table) == 63
+
+    def test_query_region_nohits(self):
+        """
+        Regression test for #2560: HEASARC returns a FITS file as a null result
+        """
+        heasarc = Heasarc()
+
+        with pytest.warns(NoResultsWarning, match='No matching rows were found in the query.'):
+            # This was an example coordinate that returned nothing
+            # Since Fermi is still active, it is possible that sometime in the
+            # future an event will occur here.
+            table = heasarc.query_region(
+                    SkyCoord(0.28136*u.deg, -0.09789*u.deg, frame='fk5'),
+                    mission='fermilpsc', radius=0.1*u.deg)
+
+        assert len(table) == 0
+        # this is to check that the header comments got parsed correctly
+        # I'm not certain that they will always be returned in the same order,
+        # so it may be necessary in the future to change this part of the test
+        assert 'heasarc_fermilpsc' in table.meta['COMMENT'][0]