raising a NotImplementedError when the row count is none

Author: shuoweil

bigframes/dataframe.py

@@ -794,6 +794,10 @@ def __repr__(self) -> str:
         pandas_df, row_count, query_job = self._block.retrieve_repr_request_results(
             max_results
         )
+        if row_count is None:
+            raise NotImplementedError(
+                "Cannot determine total number of rows. Please use .to_pandas() to display."
+            )
 
         self._set_internal_query_job(query_job)
 
@@ -879,6 +883,10 @@ def _repr_html_(self) -> str:
         pandas_df, row_count, query_job = df._block.retrieve_repr_request_results(
             max_results
         )
+        if row_count is None:
+            raise NotImplementedError(
+                "Cannot determine total number of rows. Please use .to_pandas() to display."
+            )
 
         self._set_internal_query_job(query_job)
         column_count = len(pandas_df.columns)

tests/system/small/test_anywidget.py

@@ -12,10 +12,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+
 import pandas as pd
 import pytest
 
 import bigframes as bf
+import bigframes.pandas as bpd
 
 pytest.importorskip("anywidget")
 
@@ -530,6 +532,34 @@ def test_widget_row_count_reflects_actual_data_available(
         assert widget.page_size == 2  # Respects the display option
 
 
+def test_repr_html_raises_when_row_count_is_none(monkeypatch):
+    df = bpd.DataFrame({"col1": [1, 2, 3]})
+
+    def mock_retrieve_repr_request_results(*args, **kwargs):
+        return df.to_pandas(), None, None
+
+    monkeypatch.setattr(
+        df._block, "retrieve_repr_request_results", mock_retrieve_repr_request_results
+    )
+
+    with pytest.raises(NotImplementedError):
+        df._repr_html_()
+
+
+def test_repr_raises_when_row_count_is_none(monkeypatch):
+    df = bpd.DataFrame({"col1": [1, 2, 3]})
+
+    def mock_retrieve_repr_request_results(*args, **kwargs):
+        return df.to_pandas(), None, None
+
+    monkeypatch.setattr(
+        df._block, "retrieve_repr_request_results", mock_retrieve_repr_request_results
+    )
+
+    with pytest.raises(NotImplementedError):
+        df.__repr__()
+
+
 # TODO(shuowei): Add tests for custom index and multiindex
 # This may not be necessary for the SQL Cell use case but should be
 # considered for completeness.