Logger: add a python example

logger/python/reader_example.py

+#!/usr/bin/env python3
+"""
+Read a logger file by using an index.
+Example: ./reader_example.py ../../examples/SedovBlast_3D/index.dump ../../examples/SedovBlast_3D/index_0005.hdf5
+"""
+import sys
+from h5py import File
+import numpy as np
+import matplotlib.pyplot as plt
+sys.path.append("../.libs/")
+
+import libswiftlogger as logger
+
+# Get filenames
+if len(sys.argv) != 3:
+    print("WARNING missing arguments. Will use the default ones")
+    index = "../../examples/SedovBlast_3D/index_0005.hdf5"
+    dump = "../../examples/SedovBlast_3D/index.dump"
+else:
+    index = sys.argv[-1]
+    dump = sys.argv[-2]
+
+# constant
+offset_name = "PartType0/Offset"
+header = "Header"
+time_name = "Time Offset"
+
+# Read index file
+with File(index, "r") as f:
+    if offset_name not in f:
+        raise Exception("Unable to find the offset dataset")
+    offset = f[offset_name][:]
+
+    if header not in f:
+        raise Exception("Unable to find the header")
+    if time_name not in f[header].attrs:
+        raise Exception("Unable to find the time offset")
+    time_offset = f[header].attrs[time_name]
+
+# read dump
+data = logger.loadFromIndex(offset, dump, time_offset)
+
+# Compute distance from center
+pos = data["position"]
+center = pos.mean()
+r2 = np.sum((pos - center)**2, axis=1)
+
+# plot entropy vs distance
+plt.plot(np.sqrt(r2), data["entropy"], '.')
+
+plt.xlim(0., 0.5)
+plt.ylim(-5, 50)
+plt.xlabel("Radius")
+plt.ylabel("Entropy")
+plt.show()