code: def map_midc_to_pvlib(variable_map, field_name):
      
      new_field_name = field_name
      for midc_name, pvlib_name in variable_map.items():
          if field_name.startswith(midc_name):
              # extract the instrument and units field and then remove units
              instrument_units = field_name[len(midc_name):]
              units_index = instrument_units.find('[')
              instrument = instrument_units[:units_index - 1]
              new_field_name = pvlib_name + instrument.replace(' ', '_')
              break
      return new_field_name
docs: A mapper function to rename Dataframe columns to their pvlib counterparts.
  
      Parameters
      ----------
      variable_map: Dictionary
          A dictionary for mapping MIDC field name to pvlib name. See
          VARIABLE_MAP for default value and description of how to construct
          this argument.
      field_name: string
          The Column to map.
  
      Returns
      -------
      label: string
          The pvlib variable name associated with the MIDC field or the input if
          a mapping does not exist.
  
      Notes
      -----
      Will fail if field_name to be mapped matches an entry in VARIABLE_MAP and
      does not contain brackets. This should not be an issue unless MIDC file
      headers are updated.