io: serialize 'ifo' objects in HDF5 IO

convert IFO Structs to yaml for HDF5 storage

gwinc/io.py

 import h5py
 import datetime
 
+from . import Struct
+
 
 SCHEMA = 'GWINC noise budget'
 SCHEMA_VERSION = 1
@@ -19,7 +21,13 @@ def _write_trace_recursive(grp, traces):
 
 
 def save_hdf5(path, freq, traces, **kwargs):
-    """Save GWINC traces dict to HDF5 file.
+    """Save GWINC budget data to an HDF5 file.
+
+    The `freq` argument should be the frequency array, and `traces`
+    should be the traces (recursive) dictionary.  Keyword arguments
+    are stored in the HDF5 top level 'attrs' key-value store.  If an
+    'ifo' keyword arg is supplied, it is assumed to be a Struct and
+    will be serialized to YAML for storage.
 
     See HDF5_SCHEMA.
 
@@ -30,7 +38,10 @@ def save_hdf5(path, freq, traces, **kwargs):
         # FIXME: add budget code hash or something
         f.attrs['date'] = datetime.datetime.now().isoformat()
         for key, val in kwargs.items():
-            f.attrs[key] = val
+            if key == 'ifo':
+                f.attrs['ifo'] = val.to_yaml()
+            else:
+                f.attrs[key] = val
         f.create_dataset('Freq', data=freq)
         tgrp = f.create_group('traces')
         _write_trace_recursive(tgrp, traces)
@@ -47,14 +58,19 @@ def _read_trace_recursive(element):
 
 
 def load_hdf5(path):
-    """Load traces from HDF5 file.
+    """Load GWINC budget data from an HDF5 file.
 
-    Returns a recursive traces dictionary.  See HDF5_SCHEMA.
+    Returns (freq, traces, attrs).  An 'ifo' attr will be
+    de-serialized from YAML into a Struct object.
+
+    See HDF5_SCHEMA.
 
     """
     with h5py.File(path, 'r') as f:
         # FIXME: check SCHEMA name/version
         freq = f['Freq'][:]
         traces = _read_trace_recursive(f['/traces'])
-        attrs = dict(f.attrs.items())
+        attrs = dict(f.attrs)
+        if 'ifo' in attrs:
+            attrs['ifo'] = Struct.from_yaml(attrs['ifo'])
         return freq, traces, attrs