SSB-44: using enums to specify indexes

CAL/CalibrationCommon/lib/datacontainers/holography_measurementset.py

 import os
 import re
+from enum import Enum
 
 import numpy
 from astropy.time import Time
 from casacore.tables import table as MS_Table
-
 from lofar.calibration.common.coordinates import pqr_from_icrs
+
 from .holography_dataset_definitions import *
 
 
+class CASA_POLARIZATION_INDEX(Enum):
+    XX = 0
+    XY = 1
+    YX = 2
+    YY = 3
+    X = 0
+    Y = 0
+
+
 class HolographyMeasurementSet(object):
     ms_name_pattern = r'L(?P<sas_id>\d{6})_SB(?P<sub_band_id>\d{3})_uv\.MS'
-    CASA_XX_INDEX = 0
-    CASA_XY_INDEX = 1
-    CASA_YX_INDEX = 2
-    CASA_YY_INDEX = 3
-
-    CASA_X_INDEX = 0
-    CASA_Y_INDEX = 1
 
     def __init__(self, ms_name, ms_path):
         self.path = os.path.join(ms_path, ms_name)
@@ -87,8 +90,8 @@ class HolographyMeasurementSet(object):
             tile_offsets = antenna_field_table.getcell('ELEMENT_OFFSET', station_name_index)
             tiles_not_used = antenna_field_table.getcell('ELEMENT_FLAG', station_name_index)
             index_tiles_used = numpy.where(
-                (tiles_not_used[:, HolographyMeasurementSet.CASA_X_INDEX] == False) &
-                (tiles_not_used[:, HolographyMeasurementSet.CASA_Y_INDEX] == False))[0]
+                (tiles_not_used[:, CASA_POLARIZATION_INDEX.CASA_X_INDEX] == False) &
+                (tiles_not_used[:, CASA_POLARIZATION_INDEX.CASA_Y_INDEX] == False))[0]
             tile_offsets = tile_offsets[index_tiles_used, :]
 
             axes_coordinate = antenna_field_table.getcell('COORDINATE_AXES', station_name_index)
@@ -193,16 +196,16 @@ class HolographyMeasurementSet(object):
 
                 beams_crosscorrelations_array[reference_station_index, :]['XX'] = \
                     crosscorrelations[
-                    reference_station_index, :, HolographyMeasurementSet.CASA_XX_INDEX]
+                    reference_station_index, :, CASA_POLARIZATION_INDEX.CASA_XX_INDEX]
                 beams_crosscorrelations_array[reference_station_index, :]['XY'] = \
                     crosscorrelations[
-                    reference_station_index, :, HolographyMeasurementSet.CASA_XY_INDEX]
+                    reference_station_index, :, CASA_POLARIZATION_INDEX.CASA_XY_INDEX]
                 beams_crosscorrelations_array[reference_station_index, :]['YX'] = \
                     crosscorrelations[
-                    reference_station_index, :, HolographyMeasurementSet.CASA_YX_INDEX]
+                    reference_station_index, :, CASA_POLARIZATION_INDEX.CASA_YX_INDEX]
                 beams_crosscorrelations_array[reference_station_index, :]['YY'] = \
                     crosscorrelations[
-                    reference_station_index, :, HolographyMeasurementSet.CASA_YY_INDEX]
+                    reference_station_index, :, CASA_POLARIZATION_INDEX.CASA_YY_INDEX]
 
                 beams_crosscorrelations_array[reference_station_index, :]['flag'] = \
                     flags[reference_station_index, :]
@@ -275,7 +278,7 @@ class HolographyMeasurementSet(object):
 
             return_value = numpy.empty(n_samples, dtype=return_value_dtype)
             l_m_arrays = pqr_from_icrs(numpy.array((ra, dec)), astropy_times, rotation_matrix)
-    
+
             return_value['l'][:] = l_m_arrays[:, 0]
             return_value['m'][:] = l_m_arrays[:, 1]
         else: