Disable __bool__ on DOFArray (#251)

* disable __bool__ on DOFarray

* clarify message on __bool__ error

Co-authored-by: Andreas Klöckner <[email protected]>

Co-authored-by: Andreas Klöckner <[email protected]>

Author: alexfikl

meshmode/dof_array.py

@@ -173,6 +173,11 @@ def __repr__(self):
 
     # {{{ sequence protocol
 
+    def __bool__(self):
+        raise ValueError(
+                "The truth value of a DOFArray is not well-defined. "
+                "Use actx.np.any(x) or actx.np.all(x)")
+
     def __len__(self):
         return len(self._data)