code: def parse_angular_length_quantity(string_rep, unit=u.deg):
          
          unit_mapping = {
              '"': u.arcsec,
              "'": u.arcmin,
              'd': u.deg,
              'r': u.rad,
              'i': u.dimensionless_unscaled,
              'p': u.dimensionless_unscaled
          }
          has_unit = string_rep[-1] not in string.digits
          if has_unit:
              unit = unit_mapping[string_rep[-1]]
              return u.Quantity(float(string_rep[:-1]), unit=unit)
          else:
              return u.Quantity(float(string_rep), unit=unit)
docs: Given a string that is either a number or a number and a unit, return a
          Quantity of that string.  e.g.:
  
              23.9 -> 23.9*u.deg
              50" -> 50*u.arcsec