Read from HDF with empty where throws an error (#26746)

Author: BeforeFlight

doc/source/whatsnew/v0.25.0.rst

@@ -666,6 +666,7 @@ I/O
 - Added ``cache_dates=True`` parameter to :meth:`read_csv`, which allows to cache unique dates when they are parsed (:issue:`25990`)
 - :meth:`DataFrame.to_excel` now raises a ``ValueError`` when the caller's dimensions exceed the limitations of Excel (:issue:`26051`)
 - :func:`read_excel` now raises a ``ValueError`` when input is of type :class:`pandas.io.excel.ExcelFile` and ``engine`` param is passed since :class:`pandas.io.excel.ExcelFile` has an engine defined (:issue:`26566`)
+- Bug while selecting from :class:`HDFStore` with ``where=''`` specified (:issue:`26610`).
 
 Plotting
 ^^^^^^^^

pandas/io/pytables.py

@@ -98,7 +98,7 @@ def _ensure_term(where, scope_level):
         where = wlist
     elif maybe_expression(where):
         where = Term(where, scope_level=level)
-    return where
+    return where if where is None or len(where) else None
 
 
 class PossibleDataLossError(Exception):

pandas/tests/io/test_pytables.py

@@ -4731,6 +4731,21 @@ def test_read_py2_hdf_file_in_py3(self, datapath):
             result = store['p']
             assert_frame_equal(result, expected)
 
+    @pytest.mark.parametrize("where", ["", (), (None, ), [], [None]])
+    def test_select_empty_where(self, where):
+        # GH26610
+
+        # Using keyword `where` as '' or (), or [None], etc
+        # while reading from HDF store raises
+        # "SyntaxError: only a single expression is allowed"
+
+        df = pd.DataFrame([1, 2, 3])
+        with ensure_clean_path("empty_where.h5") as path:
+            with pd.HDFStore(path) as store:
+                store.put("df", df, "t")
+                result = pd.read_hdf(store, "df", where=where)
+                assert_frame_equal(result, df)
+
 
 class TestHDFComplexValues(Base):
     # GH10447