pythoningLearning
diff --git a/‎opc/package.py‎
Lines changed: 12 additions & 0 deletions b/‎opc/package.py‎
Lines changed: 12 additions & 0 deletions
diff --git a/‎tests/test_package.py‎
Lines changed: 21 additions & 0 deletions b/‎tests/test_package.py‎
Lines changed: 21 additions & 0 deletions
@@ -66,6 +66,18 @@ def _walk_parts(rels, visited_parts=None):
         Generate exactly one reference to each of the parts in the package by
         performing a depth-first traversal of the rels graph.
         """
+        if visited_parts is None:
+            visited_parts = []
+        for rel in rels:
+            if rel.is_external:
+                continue
+            part = rel.target_part
+            if part in visited_parts:
+                continue
+            visited_parts.append(part)
+            yield part
+            for part in OpcPackage._walk_parts(part._rels, visited_parts):
+                yield part
 
 
 class Part(object):
 
@@ -81,6 +81,27 @@ def it_has_an_immutable_sequence_containing_its_parts(self):
         with patch.object(OpcPackage, '_walk_parts', return_value=parts):
             assert pkg.parts == (parts[0], parts[1])
 
+    def it_can_iterate_over_parts_by_walking_rels_graph(self):
+        # +----------+       +--------+
+        # | pkg_rels |-----> | part_1 |
+        # +----------+       +--------+
+        #      |               |    ^
+        #      v               v    |
+        #   external         +--------+
+        #                    | part_2 |
+        #                    +--------+
+        part1, part2 = (Mock(name='part1'), Mock(name='part2'))
+        part1._rels = [Mock(name='rel1', is_external=False, target_part=part2)]
+        part2._rels = [Mock(name='rel2', is_external=False, target_part=part1)]
+        pkg_rels = [
+            Mock(name='rel3', is_external=False, target_part=part1),
+            Mock(name='rel3', is_external=True),
+        ]
+        # exercise ---------------------
+        generated_parts = [part for part in OpcPackage._walk_parts(pkg_rels)]
+        # verify -----------------------
+        assert generated_parts == [part1, part2]
+
 
 class DescribePart(object):