- syntaxtree.py: added Node.index()-method

DHParser/syntaxtree.py

@@ -505,6 +505,7 @@ class Node:  # (collections.abc.Sized): Base class omitted for cython-compatibil
             if child.tag_name == tag_name:
                 return i
             i += 1
+        raise ValueError("Node with tag name '%s' not among child-nodes." % tag_name)
 
     def select(self, match_function: Callable, include_root: bool = False, reverse: bool = False) \
             -> Iterator['Node']:

test/test_syntaxtree.py

@@ -317,6 +317,17 @@ class TestNodeFind():
         assert 'c' not in tree
         assert any(tree.select_by_tag('c', False))
 
+    def test_index(self):
+        tree = parse_sxpr('(a (b 0) (c 1) (d 2))')
+        assert tree.index('d') == 2
+        assert tree.index('b') == 0
+        assert tree.index('c') == 1
+        try:
+            i = tree.index('x')
+            raise AssertionError('ValueError expected!')
+        except ValueError:
+            pass
+
 
 class TestSerialization:
     def test_sxpr_roundtrip(self):