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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 import_file(self, record, field, fname, fobj, event=None, return_format='json'):
 """ Import the contents of a file represented by fobj to a particular records field Parameters record : str record ID field : str field name where the file will go fname : str file name visible in REDCap UI fobj : file object file object as returned by `open` event : str for longitudinal projects, specify the unique event here return_format : ('json'), 'csv', 'xml' format of error message Returns ------- response : response from server as specified by ``return_format`` """

        self._check_file_field(field)
        # load up payload
        pl = self.__basepl(content='file', format=return_format)
        # no format in this call
        del pl['format']
        pl['returnFormat'] = return_format
        pl['action'] = 'import'
        pl['field'] = field
        pl['record'] = record
        if event:
            pl['event'] = event
        file_kwargs = {'files': {'file': (fname, fobj)}}
        return self._call_api(pl, 'imp_file', **file_kwargs)[0]