fixed an obscure bug in Session.binops

session1 binop session2 returned NotImplemented instead of nan for
   arrays present in session2 but not session1
This should become more relevant when we implement #514 and #515

Note that this is too obscure IMO to mention in the changelog.

Author: gdementen

larray/core/session.py

@@ -10,7 +10,7 @@
 
 from larray.core.axis import Axis
 from larray.core.array import LArray, larray_nan_equal, get_axes, ndtest, zeros, zeros_like, sequence
-from larray.util.misc import float_error_handler_factory, is_interactive_interpreter, renamed_to
+from larray.util.misc import float_error_handler_factory, is_interactive_interpreter, renamed_to, inverseop
 from larray.inout.session import check_pattern, handler_classes, ext_default_engine
 
 
@@ -662,6 +662,13 @@ def opmethod(self, other):
                     # TypeError for str arrays, ValueError for incompatible axes, ...
                     except Exception:
                         res_array = np.nan
+                    # this should only ever happen when self_array is a non Array (eg. nan)
+                    if res_array is NotImplemented:
+                        try:
+                            res_array = getattr(other_array, '__%s__' % inverseop(opname))(self_array)
+                        # TypeError for str arrays, ValueError for incompatible axes, ...
+                        except Exception:
+                            res_array = np.nan
                     res.append((name, res_array))
             return Session(res)
         opmethod.__name__ = opfullname

larray/util/misc.py

@@ -625,3 +625,18 @@ def wrapper(*args, **kwargs):
         warnings.warn(msg, FutureWarning, stacklevel=stacklevel)
         return newfunc(*args, **kwargs)
     return wrapper
+
+
+def inverseop(opname):
+    comparison_ops = {
+        'lt': 'gt',
+        'gt': 'lt',
+        'le': 'ge',
+        'ge': 'le',
+        'eq': 'eq',
+        'ne': 'ne'
+    }
+    if opname in comparison_ops:
+        return comparison_ops[opname]
+    else:
+        return 'r' + opname