code: def export_file(self, record, field, event=None, return_format='json'):
          
          self._check_file_field(field)
          # load up payload
          pl = self.__basepl(content='file', format=return_format)
          # there's no format field in this call
          del pl['format']
          pl['returnFormat'] = return_format
          pl['action'] = 'export'
          pl['field'] = field
          pl['record'] = record
          if event:
              pl['event'] = event
          content, headers = self._call_api(pl, 'exp_file')
          #REDCap adds some useful things in content-type
          if 'content-type' in headers:
              splat = [kv.strip() for kv in headers['content-type'].split(';')]
              kv = [(kv.split('=')[0], kv.split('=')[1].replace('"', '')) for kv
                    in splat if '=' in kv]
              content_map = dict(kv)
          else:
              content_map = {}
          return content, content_map
docs: Export the contents of a file stored for a particular record
  
          Notes
          -----
          Unlike other export methods, this works on a single record.
  
          Parameters
          ----------
          record : str
              record ID
          field : str
              field name containing the file to be exported.
          event: str
              for longitudinal projects, specify the unique event here
          return_format: ('json'), 'csv', 'xml'
              format of error message
  
          Returns
          -------
          content : bytes
              content of the file
          content_map : dict
              content-type dictionary