FIX-#5112: allows empty partition to be passed into `query_compiler.d…

…t_prop_map` (#5133)

Signed-off-by: Bill Wang <billiam@ponder.io>

modin/core/storage_formats/pandas/query_compiler.py

@@ -152,7 +152,11 @@ def _dt_prop_map(property_name):
 
     def dt_op_builder(df, *args, **kwargs):
         """Access specified date-time property of the passed frame."""
-        prop_val = getattr(df.squeeze(axis=1).dt, property_name)
+        squeezed_df = df.squeeze(axis=1)
+        if isinstance(squeezed_df, pandas.DataFrame) and len(squeezed_df.columns) == 0:
+            return squeezed_df
+        assert isinstance(squeezed_df, pandas.Series)
+        prop_val = getattr(squeezed_df.dt, property_name)
         if isinstance(prop_val, pandas.Series):
             return prop_val.to_frame()
         elif isinstance(prop_val, pandas.DataFrame):

modin/pandas/test/test_series.py

@@ -1733,6 +1733,22 @@ def test_dt(timezone):
     df_equals(modin_series.dt.end_time, pandas_series.dt.end_time)
     df_equals(modin_series.dt.to_timestamp(), pandas_series.dt.to_timestamp())
 
+    def dt_with_empty_partition(lib):
+        # For context, see https://github.com/modin-project/modin/issues/5112
+        df_a = lib.DataFrame({"A": [lib.to_datetime("26/10/2020")]})
+        df_b = lib.DataFrame({"B": [lib.to_datetime("27/10/2020")]})
+        df = lib.concat([df_a, df_b], axis=1)
+        eval_result = df.eval("B - A", engine="python")
+        # BaseOnPython had a single partition after the concat, and it
+        # maintains that partition after eval. In other execution modes,
+        # eval() should re-split the result into two column partitions,
+        # one of which is empty.
+        if isinstance(df, pd.DataFrame) and get_current_execution() != "BaseOnPython":
+            assert eval_result._query_compiler._modin_frame._partitions.shape == (1, 2)
+        return eval_result.dt.days
+
+    eval_general(pd, pandas, dt_with_empty_partition)
+
 
 @pytest.mark.parametrize(
     "data", test_data_with_duplicates_values, ids=test_data_with_duplicates_keys