Making Key.parent return the same instance on return calls.

This is in preparation for adding parent to the constructor. Addresses third part of #451.

Author: dhermes

gcloud/datastore/key.py

@@ -47,6 +47,7 @@ def __init__(self, path=None, namespace=None, dataset_id=None):
  **must** treat any value set by the back-end as opaque.
  """
  self._path = path or [{'kind': ''}]
+ self._parent = None
  self._namespace = namespace
  self._dataset_id = dataset_id
 
@@ -166,21 +167,35 @@ def dataset_id(self):
  """
  return self._dataset_id
 
+ def _make_parent(self):
+ """Creates a parent key for the current path.
+
+ Extracts all but the last element in the key path and creates a new
+ key, while still matching the namespace and the dataset ID.
+
+ :rtype: :class:`gcloud.datastore.key.Key` or `NoneType`
+ :returns: a new `Key` instance, whose path consists of all but the last
+ element of self's path. If self has only one path element,
+ returns None.
+ """
+ parent_path = self.path[:-1]
+ if parent_path:
+ return Key(path=parent_path, dataset_id=self.dataset_id,
+ namespace=self.namespace)
+
  @property
  def parent(self):
  """Getter: return a new key for the next highest element in path.
 
- :rtype: :class:`gcloud.datastore.key.Key`
+ :rtype: :class:`gcloud.datastore.key.Key` or `NoneType`
  :returns: a new `Key` instance, whose path consists of all but the last
  element of self's path. If self has only one path element,
  returns None.
  """
- if len(self._path) <= 1:
- return None
- # This is temporary. Will be addressed throughout #451.
- clone = self._clone()
- clone._path = self.path[:-1]
- return clone
+ if self._parent is None:
+ self._parent = self._make_parent()
+
+ return self._parent
 
  def __repr__(self):
  return '<Key%s>' % self.path

gcloud/datastore/test_key.py

@@ -186,3 +186,14 @@ def test_parent_explicit_nested(self):
  {'kind': 'ghi', 'id': 123},
  ])
  self.assertEqual(key.parent.path, [parent_part])
+
+ def test_parent_multiple_calls(self):
+ _PARENT_KIND = 'KIND1'
+ _PARENT_ID = 1234
+ _PARENT_PATH = {'kind': _PARENT_KIND, 'id': _PARENT_ID}
+ _PATH = [_PARENT_PATH, {'kind': 'KIND2'}]
+ key = self._makeOne(path=_PATH)
+ parent = key.parent
+ self.assertEqual(parent.path, [_PARENT_PATH])
+ new_parent = key.parent
+ self.assertTrue(parent is new_parent)