[h5dataset] Catch H5Py indexing ValueError

H5Py throws ValueError for out-of-bounds indexing. We catch it and throw
IndexError instead, reusing the error message from H5Py.

This also makes indexing more flexible. Slices now work the same as in
numpy, so no slice is ever out-of-bounds. The corresponding test has
been updated accordingly.

This is an updated version of PR G-Node#303, which was a fix for G-Node#299.

nixio/hdf5/h5dataset.py

@@ -45,7 +45,12 @@ def write_data(self, data, sl=None):
     def read_data(self, sl=None):
         if sl is None:
             return self.dataset[:]
-        return self.dataset[sl]
+        try:
+            return self.dataset[sl]
+        except ValueError as ve:
+            # h5py throws ValueError for out-of-bounds index
+            # Let's change it to IndexError
+            raise IndexError(ve)
 
     def set_attr(self, name, value):
         if value is None:

nixio/test/test_data_array.py

@@ -415,7 +415,7 @@ def test_outofbounds_indexing(self):
         with self.assertRaises(IndexError):
             oobtestda[10]
         with self.assertRaises(IndexError):
-            oobtestda[1:4]
+            oobtestda[-7]
 
     def test_data_array_numpy_indexing(self):
         data = np.random.rand(50)