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BUG: Unhandled ValueError when Bigquery called through io.gbq returns zero rows #10273 #10274

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BUG: Unhandled ValueError when Bigquery called through io.gbq returns zero rows #10273 #10274

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1 change: 1 addition & 0 deletions doc/source/whatsnew/v0.17.0.txt
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Expand Up @@ -678,3 +678,4 @@ Bug Fixes
- Bug in ``iloc`` allowing memory outside bounds of a Series to be accessed with negative integers (:issue:`10779`)
- Bug in ``read_msgpack`` where encoding is not respected (:issue:`10580`)
- Bug preventing access to the first index when using ``iloc`` with a list containing the appropriate negative integer (:issue:`10547`, :issue:`10779`)
- Bug where ``pd.read_gbq`` throws ``ValueError`` when Bigquery returns zero rows (:issue:`10273`)
7 changes: 5 additions & 2 deletions pandas/io/gbq.py
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Expand Up @@ -279,7 +279,7 @@ def _parse_data(schema, rows):
field_type)
page_array[row_num][col_num] = field_value

return DataFrame(page_array)
return DataFrame(page_array, columns=col_names)
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this should not be necessary, page_array is already a record array (this will just reindex it) (and copy it).


def _parse_entry(field_value, field_type):
if field_value is None or field_value == 'null':
Expand Down Expand Up @@ -338,7 +338,10 @@ def read_gbq(query, project_id=None, index_col=None, col_order=None, reauth=Fals
page = pages.pop()
dataframe_list.append(_parse_data(schema, page))

final_df = concat(dataframe_list, ignore_index = True)
if len(dataframe_list)>0:
final_df = concat(dataframe_list, ignore_index = True)
else:
final_df = _parse_data(schema,[])
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This makes it necessary. Since we are constructing blank dataframe, no data is added in dataframe. But it should pick the output schema from query response received from bigquery.


# Reindex the DataFrame on the provided column
if index_col is not None:
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7 changes: 7 additions & 0 deletions pandas/io/tests/test_gbq.py
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Expand Up @@ -296,6 +296,13 @@ def test_download_dataset_larger_than_200k_rows(self):
df = gbq.read_gbq("SELECT id FROM [publicdata:samples.wikipedia] GROUP EACH BY id ORDER BY id ASC LIMIT 200005", project_id=PROJECT_ID)
self.assertEqual(len(df.drop_duplicates()), 200005)

def test_zero_rows(self):
# Bug fix for https://github.com/pydata/pandas/issues/10273
df = gbq.read_gbq("SELECT title, language FROM [publicdata:samples.wikipedia] where timestamp=-9999999", project_id=PROJECT_ID)
expected_result = DataFrame(columns=['title', 'language'])
self.assert_frame_equal(df, expected_result)


class TestToGBQIntegration(tm.TestCase):
# This class requires bq.py to be installed for setup/teardown.
# It will also need to be preconfigured with a default dataset,
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