Added automatic ref and deref to SddNode wrapper. (#44)

Author: VincentDerk

pysdd/sdd.pyx

@@ -53,6 +53,7 @@ cdef class SddNode:
         wrapper._sddnode = node
         if wrapper.garbage_collected():
             return None
+        wrapper.ref()
         if sddapi_c.sdd_node_is_literal(node):
             wrapper._name = sddapi_c.sdd_node_literal(node)
         elif sddapi_c.sdd_node_is_true(node):
@@ -63,6 +64,9 @@ cdef class SddNode:
             wrapper._name = "Decision"
         return wrapper
 
+    def __del__(self):
+        # clean up _sddnode ref
+        self.deref()
 
     @property
     def id(self):
@@ -306,7 +310,6 @@ cdef class SddNode:
 
         Returns the node.
         """
-        # TODO: Should we ref every Python SDDNode object on creation and deref on Python GC?
         sddapi_c.sdd_ref(self._sddnode, self._manager._sddmanager)
 
     def deref(self):

tests/test_minimize.py

@@ -74,6 +74,22 @@ def test_min2():
         # with (directory / "sdd2_before_b.gv").open("w") as out:
         #     print(sdd_to_dot(sdd), file=out)
 
+def test_refcount():
+    sdd = SddManager(var_count=2)
+    a, b = sdd.vars
+    f = a | b
+    assert f.ref_count() == 1
+    f.ref()
+    assert f.ref_count() == 2
+    f.deref()
+    assert f.ref_count() == 1
+    # equivalent formula will
+    # ref same formula object
+    f2 = b | a
+    assert f2.ref_count() == 2
+    assert f.ref_count() == 2
+    del f2
+    assert f.ref_count() == 1
 
 if __name__ == "__main__":
     logger.setLevel(logging.DEBUG)