Add public accessor to UDF/UDX node parents

Resolves #245

CHANGELOG.md

@@ -10,6 +10,8 @@ these changes are prefixed with "**BREAKING**"
 ### Added
 
 * `requirements.txt` mainly to try and help GitHub detect dependencies
+* `delphin.derivation.UDFNode.parent` ([#245][])
+* `delphin.derivation.UDFTerminal.parent` ([#245][])
 
 ### Changed
 
@@ -1196,6 +1198,7 @@ information about changes, except for
 [#200]: https://github.com/delph-in/pydelphin/issues/200
 [#203]: https://github.com/delph-in/pydelphin/issues/203
 [#213]: https://github.com/delph-in/pydelphin/issues/213
+[#245]: https://github.com/delph-in/pydelphin/issues/245
 [#247]: https://github.com/delph-in/pydelphin/issues/247
 [#248]: https://github.com/delph-in/pydelphin/issues/248
 [#249]: https://github.com/delph-in/pydelphin/issues/249

delphin/derivation.py

@@ -75,6 +75,10 @@ def __ne__(self, other):
             return NotImplemented
         return not (self == other)
 
+    @property
+    def parent(self):
+        return self._parent
+
     # serialization
 
     def to_udf(self, indent=1):

docs/api/delphin.derivation.rst

@@ -142,6 +142,12 @@ delphin.derivation
 
          The lexical type (available on preterminal UDX nodes).
 
+      .. py:attribute:: parent
+
+	 The parent node in the tree, or ``None`` for the root. Note
+	 that this is not a regular UDF/UDX attribute but is added for
+	 convenience in traversing the tree.
+
       .. automethod:: is_root
       .. automethod:: to_udf
       .. automethod:: to_udx
@@ -158,6 +164,12 @@ delphin.derivation
 
          The list of tokens.
 
+      .. py:attribute:: parent
+
+	 The parent node in the tree. Note that this is not a regular
+	 UDF/UDX attribute but is added for convenience in traversing
+	 the tree.
+
       .. automethod:: is_root
       .. automethod:: to_udf
       .. automethod:: to_udx

tests/derivation_test.py

@@ -33,6 +33,12 @@ def test_init(self):
         assert n.is_head()
         assert n.type == 'type'
 
+    def test_parent(self):
+        n1 = N(None, 'entity')
+        assert n1.parent is None
+        n2 = N(1, 'entity', 0.5, 1, 2, [], head=True, type='type', parent=n1)
+        assert n2.parent is n1
+
 
 class TestDerivation():
     def test_init(self):