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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def dataframe(start_row=0, max_rows=None, use_cache=True):
 """ Construct a query output object where the result is a dataframe Args: start_row: the row of the table at which to start the export (default 0). max_rows: an upper limit on the number of rows to export (default None). use_cache: whether to use cached results or not (default True). """

    output = QueryOutput()
    output._output_type = 'dataframe'
    output._dataframe_start_row = start_row
    output._dataframe_max_rows = max_rows
    output._use_cache = use_cache
    return output