def encode_chunk(dataframe):
    """Return a file-like object of CSV-encoded rows.

    Args:
      dataframe (pandas.DataFrame): A chunk of a dataframe to encode
    """
    csv_buffer = io.StringIO()
    dataframe.to_csv(
        csv_buffer,
        index=False,
        header=False,
        encoding="utf-8",
        float_format="%.17g",
        date_format="%Y-%m-%d %H:%M:%S.%f",
    )

    # Convert to a BytesIO buffer so that unicode text is properly handled.
    # See: https://github.com/pydata/pandas-gbq/issues/106
    body = csv_buffer.getvalue()
    body = body.encode("utf-8")
    return io.BytesIO(body)
Return a file-like object of CSV-encoded rows.

    Args:
      dataframe (pandas.DataFrame): A chunk of a dataframe to encode
    
pandas_gbq/load/core.py