SSB-47: checking speed without reading data

CAL/CalibrationCommon/lib/datacontainers/holography_dataset.py

 import logging
 import os
-
 import h5py
-from lofar.calibration.common.datacontainers.holography_observation import HolographyObservation
 
 from .holography_dataset_definitions import *
 from .holography_specification import HolographySpecification
-
+from .holography_observation import HolographyObservation
 
 logger = logging.getLogger(__file__)
 
@@ -544,13 +542,52 @@ class HolographyDataset():
     @staticmethod
     def load_from_file(path):
         """
-        It reads a holography dataset from an HDF5 file and returns a
+        Read a holography dataset from an HDF5 file and returns a
         HolographyDataset class
         :param path: path to file
         :return: the read dataset
         """
         f = None
 
+        try:
+            result, f = HolographyDataset.open_holography_file(path)
+
+            result.data = dict()
+            for reference_station in f["CROSSCORRELATION"].keys():
+                for frequency in f["CROSSCORRELATION"][reference_station].keys():
+                    for beamlet in f["CROSSCORRELATION"][reference_station][frequency].keys():
+                        if reference_station not in result.data:
+                            result.data[reference_station] = dict()
+                        if frequency not in result.data[reference_station]:
+                            result.data[reference_station][frequency] = dict()
+                        result.data[reference_station][frequency][beamlet] = numpy.array(
+                            f["CROSSCORRELATION"][reference_station][frequency][beamlet])
+
+            if '/DERIVED_DATA' in f:
+                result.derived_data = HolographyDataset._read_grouped_data(f, '/DERIVED_DATA')
+        except Exception as e:
+            logger.exception(
+                "Cannot read the Holography Data Set data from the HDF5 file \"%s\"."
+                " This is the exception that was thrown:  %s",
+                path, e)
+            raise e
+        finally:
+            if f is not None:
+                f.close()
+
+        return result
+
+    @staticmethod
+    def open_holography_file(path: str):
+        """
+        Opens the Holography HDF file for access and returns the Holography Dataset and
+        it's file descriptor
+        :param path: path to file
+        :return: the read dataset
+        :rtype: List[HolographyDataset, h5py.File]
+        """
+        f = None
+
         if not os.path.exists(path):
             raise FileNotFoundError(path)
 
@@ -584,32 +621,26 @@ class HolographyDataset():
                     result.ra_dec[frequency][beamlet] = numpy.array(f["RA_DEC"][frequency][beamlet])
 
             beamlets = set()
-            result.data = dict()
             for reference_station in f["CROSSCORRELATION"].keys():
                 for frequency in f["CROSSCORRELATION"][reference_station].keys():
                     for beamlet in f["CROSSCORRELATION"][reference_station][frequency].keys():
                         beamlets.add(int(beamlet))
-                        if reference_station not in result.data:
-                            result.data[reference_station] = dict()
-                        if frequency not in result.data[reference_station]:
-                            result.data[reference_station][frequency] = dict()
-                        result.data[reference_station][frequency][beamlet] = numpy.array(
-                            f["CROSSCORRELATION"][reference_station][frequency][beamlet])
+
+            result.data = f['CROSSCORRELATION']
 
             result.central_beamlets = HolographyDataset._read_grouped_data(f, HDS_CENTRAL_BEAMLETS)
 
             if '/DERIVED_DATA' in f:
-                result.derived_data = HolographyDataset._read_grouped_data(f, '/DERIVED_DATA')
+                result.derived_data = f['/DERIVED_DATA']
+
         except Exception as e:
             logger.exception(
-                "Cannot read the Holography Data Set data from the HDF5 file \"%s\".  This is the exception that was thrown:  %s",
+                "Cannot read the Holography Data Set data from the HDF5 file \"%s\"."
+                " This is the exception that was thrown:  %s",
                 path, e)
             raise e
-        finally:
-            if f is not None:
-                f.close()
 
-        return result
+        return result, f
 
     def store_to_file(self, path):
         """
@@ -679,7 +710,8 @@ class HolographyDataset():
 
         except Exception as e:
             logger.exception(
-                "Cannot write the Holography Data Set data to the HDF5 file \"%s\".  This is the exception that was thrown:  %s",
+                "Cannot write the Holography Data Set data to the HDF5 file \"%s\"."
+                " This is the exception that was thrown:  %s",
                 path, e)
             raise e
         finally: