FIX: attribute access for the obsolete background attributes.

- Do not raise AttributeError inside a property getter (use RuntimeError)
- Add test

fretbursts/burstlib.py

@@ -1355,10 +1355,14 @@ def _obsolete_bg_attr(self, attrname, ph_sel):
             bg_field = 'bg'
         elif attrname in bg_mean_attrs:
             bg_field = 'bg_mean'
-        if bg_field in self:
-            return getattr(self, bg_field)[ph_sel]
-        else:
-            raise AttributeError('No attribute `%s` found in Data.' % bg_field)
+        try:
+            value = getattr(self, bg_field)[ph_sel]
+        except AttributeError as e:
+            # This only happens when trying to access 'bg' because
+            # 'bg_mean' raises RuntimeError when missing.
+            msg = 'No attribute `%s` found. Please compute background first.'
+            raise RuntimeError(msg % bg_field) from e
+        return value
 
     @property
     def rate_m(self):
@@ -1629,7 +1633,7 @@ def nperiods(self):
     @property
     def bg_mean(self):
         if 'bg' not in self:
-            raise AttributeError('No background found, compute it first.')
+            raise RuntimeError('No background found, compute it first.')
         if not hasattr(self, '_bg_mean'):
             self._bg_mean = {k: [bg_ch.mean() for bg_ch in bg_ph_sel]
                              for k, bg_ph_sel in self.bg.items()}

fretbursts/tests/test_burstlib.py

@@ -97,6 +97,19 @@ def list_array_allclose(list1, list2):
 # Test functions
 #
 
+
+def test_bg_compatlayer_for_obsolete_attrs():
+    d = load_dataset_1ch(process=False)
+    attrs = ('bg_dd', 'bg_ad', 'bg_da', 'bg_aa',
+             'rate_m', 'rate_dd', 'rate_ad', 'rate_da', 'rate_aa')
+    for attr in attrs:
+        with pytest.raises(RuntimeError):
+            getattr(d, attr)
+    _alex_process(d)
+    for attr in attrs:
+        assert isinstance(getattr(d, attr), list)
+
+
 def test_ph_times_compact(data_1ch):
     """Test calculation of ph_times_compact."""
     def isinteger(x):
@@ -156,7 +169,7 @@ def test_bg_calc(data):
     assert 'bg_auto_th_us0' in data
     assert 'bg_auto_F_bg' in data
     assert 'bg_th_us_user' not in data
-    
+
     data.calc_bg(bg.exp_fit, time_s=30, tail_min_us='auto', F_bg=1.7,
                  fit_allph=False)
     streams = [s for s in data.ph_streams if s != Ph_sel('all')]