fix: calling info() on empty dataframes no longer leads to errors (#2267)

Fixes #460154155 🦕

Author: sycai

bigframes/dataframe.py

@@ -521,15 +521,21 @@ def info(
 ifself._block.has_index:
 index_type="MultiIndex"ifself.index.nlevels>1else"Index"
 
-# These accessses are kind of expensive, maybe should try to skip?
-first_indice=self.index[0]
-last_indice=self.index[-1]
-obuf.write(
-f"{index_type}: {n_rows} entries, {first_indice} to {last_indice}\n"
- )
+index_stats=f"{n_rows} entries"
+ifn_rows>0:
+# These accessses are kind of expensive, maybe should try to skip?
+first_indice=self.index[0]
+last_indice=self.index[-1]
+index_stats+=f", {first_indice} to {last_indice}"
+obuf.write(f"{index_type}: {index_stats}\n")
 else:
 obuf.write("NullIndex\n")
 
+ifn_columns==0:
+# We don't display any more information if the dataframe has no columns
+obuf.write("Empty DataFrame\n")
+return
+
 dtype_strings=self.dtypes.astype("string")
 ifshow_all_columns:
 obuf.write(f"Data columns (total {n_columns} columns):\n")

tests/system/small/test_dataframe.py

@@ -671,15 +671,61 @@ def test_df_info(scalars_dfs):
 "dtypes: Float64(1), Int64(3), binary[pyarrow](1), boolean(1), date32[day][pyarrow](1), decimal128(38, 9)[pyarrow](1), duration[us][pyarrow](1), geometry(1), string(1), time64[us][pyarrow](1), timestamp[us, tz=UTC][pyarrow](1), timestamp[us][pyarrow](1)\n"
 "memory usage: 1341 bytes\n"
  )
-
 scalars_df, _=scalars_dfs
-bf_result=io.StringIO()
 
+bf_result=io.StringIO()
 scalars_df.info(buf=bf_result)
 
 assertexpected==bf_result.getvalue()
 
 
+deftest_df_info_no_rows(session):
+expected= (
+"<class 'bigframes.dataframe.DataFrame'>\n"
+"Index: 0 entries\n"
+"Data columns (total 1 columns):\n"
+" # Column Non-Null Count Dtype\n"
+"--- -------- ---------------- -------\n"
+" 0 col 0 non-null Float64\n"
+"dtypes: Float64(1)\n"
+"memory usage: 0 bytes\n"
+ )
+df=session.DataFrame({"col": []})
+
+bf_result=io.StringIO()
+df.info(buf=bf_result)
+
+assertexpected==bf_result.getvalue()
+
+
+deftest_df_info_no_cols(session):
+expected= (
+"<class 'bigframes.dataframe.DataFrame'>\n"
+"Index: 3 entries, 1 to 3\n"
+"Empty DataFrame\n"
+ )
+df=session.DataFrame({}, index=[1, 2, 3])
+
+bf_result=io.StringIO()
+df.info(buf=bf_result)
+
+assertexpected==bf_result.getvalue()
+
+
+deftest_df_info_no_cols_no_rows(session):
+expected= (
+"<class 'bigframes.dataframe.DataFrame'>\n"
+"Index: 0 entries\n"
+"Empty DataFrame\n"
+ )
+df=session.DataFrame({})
+
+bf_result=io.StringIO()
+df.info(buf=bf_result)
+
+assertexpected==bf_result.getvalue()
+
+
 @pytest.mark.parametrize(
  ("include", "exclude"),
  [