>>> cursor.execute("select 'foo %'")
>>> cursor.fetchall()
[Row(('foo %',), {'f0_': 0})]
>>> cursor.execute("select 'foo %'", dict(x=1))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/jim/p/g/python-bigquery/google/cloud/bigquery/dbapi/_helpers.py", line 273, in with_closed_check
    return method(self, *args, **kwargs)
  File "/home/jim/p/g/python-bigquery/google/cloud/bigquery/dbapi/cursor.py", line 172, in execute
    formatted_operation = _format_operation(operation, parameters=parameters)
  File "/home/jim/p/g/python-bigquery/google/cloud/bigquery/dbapi/cursor.py", line 460, in _format_operation
    return _format_operation_dict(operation, parameters)
  File "/home/jim/p/g/python-bigquery/google/cloud/bigquery/dbapi/cursor.py", line 434, in _format_operation_dict
    return operation % formatted_params
ValueError: unsupported format character ''' (0x27) at index 13