code: def parse_angular_length_quantity(string_rep):
          
          unit_mapping = {
              'deg': u.deg,
              'rad': u.rad,
              'arcmin': u.arcmin,
              'arcsec': u.arcsec,
              'pix': u.dimensionless_unscaled,
              '"': u.arcsec,
              "'": u.arcmin,
          }
          regex_str = re.compile(r'([0-9+,-.]*)(.*)')
          str = regex_str.search(string_rep)
          unit = str.group(2)
          if unit:
              if unit in unit_mapping:
                  return u.Quantity(str.group(1), unit=unit_mapping[unit])
              return u.Quantity(str.group(1))
          else:
              raise CRTFRegionParserError('Units must be specified for {0} '.format(string_rep))
docs: Given a string that is a number and a unit, return a
          Quantity of that string.Raise an Error If there is no unit.  e.g.:
              50" -> 50*u.arcsec
              50 -> CRTFRegionParserError : Units must be specified for 50