Propagate exceptions during type conversion (#4911)

Release 4.2.0 generalized the use of utility functions to convert
Python vector-valued objects of size 3 to the corresponding C++
script interface Vector3d or Vector3i types. Exceptions raised in
these functions were not propagated to the Python interpreter,
printing "Exception ignored in: 'espressomd.utils.make_Vector3d'"
to the screen and leaving the call site with a fully or partially
uninitialized object. This is now resolved.

Author: jngrad

src/python/espressomd/utils.pxd

@@ -105,8 +105,8 @@ cdef extern from "utils/quaternion.hpp" namespace "Utils":
 
 cdef make_array_locked(Vector3d)
 cdef make_array_locked_vector(vector[Vector3d] v)
-cdef Vector3d make_Vector3d(a)
-cdef Vector3i make_Vector3i(a)
+cdef Vector3d make_Vector3d(a) except *
+cdef Vector3i make_Vector3i(a) except *
 
 cdef extern from "utils/Factory.hpp" namespace "Utils":
     cdef cppclass Factory[T]:

src/python/espressomd/utils.pyx

@@ -241,15 +241,17 @@ cdef make_array_locked_vector(vector[Vector3d] v):
     return array_locked(ret)
 
 
-cdef Vector3d make_Vector3d(a):
+cdef Vector3d make_Vector3d(a) except *:
     cdef Vector3d v
+    assert len(a) == 3
     for i, ai in enumerate(a):
         v[i] = ai
     return v
 
 
-cdef Vector3i make_Vector3i(a):
+cdef Vector3i make_Vector3i(a) except *:
     cdef Vector3i v
+    assert len(a) == 3
     for i, ai in enumerate(a):
         v[i] = ai
     return v

testsuite/python/lb.py

@@ -107,6 +107,12 @@ def test_properties(self):
             lbf[0, 0, 0].velocity = [1, 2]
         with self.assertRaises(Exception):
             lbf[0, 1].velocity = [1, 2, 3]
+        with self.assertRaises(TypeError):
+            lbf.ext_force_density = 0
+        with self.assertRaises(AssertionError):
+            lbf.ext_force_density = [1, 2]
+        with self.assertRaises(AssertionError):
+            lbf.ext_force_density = [1, 2, 3, 4]
 
     def test_raise_if_not_active(self):
         class MockLBFluid(self.lb_class):