FIX: raise error in ExprNode.__bool__ instead of returning True

gdementen · gdementen · commit 3796f9baf80a · 2023-10-23T16:02:41.000+02:00
diff --git a/doc/source/changes/version_0_34_2.rst.inc b/doc/source/changes/version_0_34_2.rst.inc
@@ -62,3 +62,11 @@ Fixes
 * Array.split_axes now raises an explicit error when some labels contain
   more separators than others, instead of silently dropping part of those
   labels, or even some data (closes :issue:`1089`).
+
+* a boolean condition including only X.axes_name and scalars (e.g. X.age == 0)
+  raises an error when Python needs to know whether it is True or not (because
+  there is no array to extract the axis labels from) instead of always
+  evaluating to True. This was especially dangerous in the context of a
+  where() function, which always evaluated to its left side
+  (e.g. where(X.age > 0, arr, 0) evaluated to 'arr' for all ages).
+  Closes :issue:`1083`.
diff --git a/larray/core/expr.py b/larray/core/expr.py
@@ -1,4 +1,7 @@
 class ExprNode:
+    def __bool__(self):
+        raise ValueError("Cannot evaluate the truth value of an expression using X.axis_name")
+
     # method factory
     def _binop(opname):
         def opmethod(self, other):
diff --git a/larray/tests/test_array.py b/larray/tests/test_array.py
@@ -2945,6 +2945,11 @@ def test_unary_ops(small_array):
     assert_nparray_equal((~small_array).data, ~raw)
 
 
+def test_binary_ops_expressions():
+    with must_raise(ValueError, "Cannot evaluate the truth value of an expression using X.axis_name"):
+        res = 0 if X.age == 3 else 1
+
+
 def test_mean(small_array):
     raw = small_array.data
     c, d = small_array.axes
