feat: add a warning on empty response

Author: ManonMarchand

astroquery/simbad/core.py

@@ -18,7 +18,7 @@
 
 from astroquery.query import BaseVOQuery
 from astroquery.utils import commons
-from astroquery.exceptions import LargeQueryWarning
+from astroquery.exceptions import LargeQueryWarning, NoResultsWarning
 from astroquery.simbad.utils import (_catch_deprecated_fields_with_arguments,
                                      _wildcard_to_regexp, CriteriaTranslator,
                                      query_criteria_fields)
@@ -1397,7 +1397,7 @@ def _query(self, top, columns, joins, criteria, from_table="basic",
         `~astropy.table.Table`
             The result of the query to SIMBAD.
         """
-        top = f" TOP {top}" if top != -1 else ""
+        top_part = f" TOP {top}" if top != -1 else ""
 
         # columns
         input_columns = [f'{column.table}."{column.name}" AS "{column.alias}"' if column.alias is not None
@@ -1425,9 +1425,16 @@ def _query(self, top, columns, joins, criteria, from_table="basic",
         else:
             criteria = ""
 
-        query = f"SELECT{top}{columns} FROM {from_table}{join}{criteria}"
+        query = f"SELECT{top_part}{columns} FROM {from_table}{join}{criteria}"
 
-        return self.query_tap(query, get_query_payload=get_query_payload, **uploads)
+        response = self.query_tap(query, get_query_payload=get_query_payload,
+                                  maxrec=self.hardlimit,
+                                  **uploads)
+
+        if len(response) == 0 and top != 0:
+            warnings.warn("The request executed correctly, but there was no data corresponding"
+                          " to these criteria in SIMBAD", NoResultsWarning)
+        return response
 
 
 Simbad = SimbadClass()

astroquery/simbad/tests/test_simbad.py

@@ -13,7 +13,7 @@
 
 from ... import simbad
 from .test_simbad_remote import multicoords
-from astroquery.exceptions import LargeQueryWarning
+from astroquery.exceptions import LargeQueryWarning, NoResultsWarning
 
 
 GALACTIC_COORDS = SkyCoord(l=-67.02084 * u.deg, b=-29.75447 * u.deg, frame="galactic")
@@ -486,6 +486,16 @@ def test_query_tap_cache_call(monkeypatch):
     assert simbad.Simbad.query_tap("select top 1 * from basic") == msg
 
 
+@pytest.mark.usefixtures("_mock_simbad_class")
+def test_empty_response_warns(monkeypatch):
+    # return something of length zero
+    monkeypatch.setattr(simbad.core.Simbad, "query_tap", lambda _, get_query_payload, maxrec: [])
+    msg = ("The request executed correctly, but there was no data corresponding to these"
+           " criteria in SIMBAD")
+    with pytest.warns(NoResultsWarning, match=msg):
+        simbad.core.Simbad.query_catalog("unknown_catalog")
+
+
 # ---------------------------------------------------
 # Test the adql string for query_tap helper functions
 # ---------------------------------------------------

astroquery/simbad/tests/test_simbad_remote.py

@@ -6,6 +6,7 @@
 from astropy.utils.exceptions import AstropyDeprecationWarning
 from astropy.table import Table
 
+from astroquery.exceptions import NoResultsWarning
 from astroquery.simbad import Simbad
 from astroquery.simbad.core import _cached_query_tap, _Column, _Join
 
@@ -141,6 +142,11 @@ def test_query_tap(self):
         Simbad.clear_cache()
         assert _cached_query_tap.cache_info().currsize == 0
 
+    def test_empty_response_warns(self):
+        with pytest.warns(NoResultsWarning, match="The request executed correctly, but *"):
+            # a catalog that does not exists should return an empty response
+            Simbad.query_catalog("unknown_catalog")
+
     # ----------------------------------
 
     def test_simbad_list_tables(self):