Adding lazy loading support for dataset ID.

gcloud/datastore/_implicit_environ.py

@@ -33,22 +33,6 @@
 _GCD_DATASET_ENV_VAR_NAME = 'DATASTORE_DATASET'
 
 
-class _DefaultsContainer(object):
-    """Container for defaults.
-
-    :type connection: :class:`gcloud.datastore.connection.Connection`
-    :param connection: Persistent implied connection from environment.
-
-    :type dataset_id: string
-    :param dataset_id: Persistent implied dataset ID from environment.
-    """
-
-    def __init__(self, connection=None, dataset_id=None, implicit=False):
-        self.implicit = implicit
-        self.connection = connection
-        self.dataset_id = dataset_id
-
-
 def app_engine_id():
     """Gets the App Engine application ID if it can be inferred.
 
@@ -150,6 +134,15 @@ def set_default_dataset_id(dataset_id=None):
         raise EnvironmentError('No dataset ID could be inferred.')
 
 
+def get_default_dataset_id():
+    """Get default dataset ID.
+
+    :rtype: string or ``NoneType``
+    :returns: The default dataset ID if one has been set.
+    """
+    return _DEFAULTS.dataset_id
+
+
 def get_default_connection():
     """Get default connection.
 
@@ -159,13 +152,69 @@ def get_default_connection():
     return _DEFAULTS.connection
 
 
-def get_default_dataset_id():
-    """Get default dataset ID.
+class _LazyProperty(object):
+    """Descriptor for lazy loaded property.
 
-    :rtype: string or ``NoneType``
-    :returns: The default dataset ID if one has been set.
+    This follows the reify pattern: lazy evaluation and then replacement
+    after evaluation.
+
+    :type name: string
+    :param name: The name of the attribute / property being evaluated.
+
+    :type deferred_callable: callable that takes no arguments
+    :param deferred_callable: The function / method used to evaluate the
+                              property.
     """
-    return _DEFAULTS.dataset_id
+
+    def __init__(self, name, deferred_callable):
+        self._name = name
+        self._deferred_callable = deferred_callable
+
+    def __get__(self, obj, objtype):
+        if obj is None or objtype is not _DefaultsContainer:
+            return self
+
+        setattr(obj, self._name, self._deferred_callable())
+        return getattr(obj, self._name)
+
+
+def _lazy_property_deco(deferred_callable):
+    """Decorator a method to create a :class:`_LazyProperty`.
+
+    :type deferred_callable: callable that takes no arguments
+    :param deferred_callable: The function / method used to evaluate the
+                              property.
+
+    :rtype: :class:`_LazyProperty`.
+    :returns: A lazy property which defers the deferred_callable.
+    """
+    if isinstance(deferred_callable, staticmethod):
+        # H/T: http://stackoverflow.com/a/9527450/1068170
+        #      For Python2.7+ deferred_callable.__func__ would suffice.
+        deferred_callable = deferred_callable.__get__(True)
+    return _LazyProperty(deferred_callable.__name__, deferred_callable)
+
+
+class _DefaultsContainer(object):
+    """Container for defaults.
+
+    :type connection: :class:`gcloud.datastore.connection.Connection`
+    :param connection: Persistent implied connection from environment.
+
+    :type dataset_id: string
+    :param dataset_id: Persistent implied dataset ID from environment.
+    """
+
+    @_lazy_property_deco
+    @staticmethod
+    def dataset_id():
+        """Return the implicit default dataset ID."""
+        return _determine_default_dataset_id()
+
+    def __init__(self, connection=None, dataset_id=None, implicit=False):
+        self.connection = connection
+        if dataset_id is not None or not implicit:
+            self.dataset_id = dataset_id
 
 
 _DEFAULTS = _DefaultsContainer(implicit=True)

gcloud/datastore/_testing.py

@@ -24,9 +24,9 @@ def _monkey_defaults(*args, **kwargs):
     return _Monkey(_implicit_environ, _DEFAULTS=mock_defaults)
 
 
-def _setup_defaults(test_case):
+def _setup_defaults(test_case, *args, **kwargs):
     test_case._replaced_defaults = _implicit_environ._DEFAULTS
-    _implicit_environ._DEFAULTS = _DefaultsContainer()
+    _implicit_environ._DEFAULTS = _DefaultsContainer(*args, **kwargs)
 
 
 def _tear_down_defaults(test_case):

gcloud/datastore/test__implicit_environ.py

@@ -321,6 +321,82 @@ def test_set_implicit_three_env_appengine_and_compute(self):
         self.assertEqual(connection.timeout, None)
 
 
+class Test__lazy_property_deco(unittest2.TestCase):
+
+    def _callFUT(self, deferred_callable):
+        from gcloud.datastore._implicit_environ import _lazy_property_deco
+        return _lazy_property_deco(deferred_callable)
+
+    def test_on_function(self):
+        def test_func():
+            pass  # pragma: NO COVER never gets called
+
+        lazy_prop = self._callFUT(test_func)
+        self.assertTrue(lazy_prop._deferred_callable is test_func)
+        self.assertEqual(lazy_prop._name, 'test_func')
+
+    def test_on_staticmethod(self):
+        def test_func():
+            pass  # pragma: NO COVER never gets called
+
+        lazy_prop = self._callFUT(staticmethod(test_func))
+        self.assertTrue(lazy_prop._deferred_callable is test_func)
+        self.assertEqual(lazy_prop._name, 'test_func')
+
+
+class Test_lazy_loaded_dataset_id(unittest2.TestCase):
+
+    def setUp(self):
+        from gcloud.datastore._testing import _setup_defaults
+        _setup_defaults(self, implicit=True)
+
+    def tearDown(self):
+        from gcloud.datastore._testing import _tear_down_defaults
+        _tear_down_defaults(self)
+
+    def test_prop_default(self):
+        from gcloud.datastore import _implicit_environ
+        from gcloud.datastore._implicit_environ import _DefaultsContainer
+        from gcloud.datastore._implicit_environ import _LazyProperty
+
+        self.assertTrue(isinstance(_DefaultsContainer.dataset_id,
+                                   _LazyProperty))
+        self.assertEqual(_implicit_environ._DEFAULTS.dataset_id, None)
+
+    def test_prop_on_wrong_class(self):
+        from gcloud.datastore._implicit_environ import _LazyProperty
+
+        # Don't actually need a callable for ``method`` since
+        # __get__ will just return ``self`` in this test.
+        data_prop = _LazyProperty('dataset_id', None)
+
+        class FakeEnv(object):
+            dataset_id = data_prop
+
+        self.assertTrue(FakeEnv.dataset_id is data_prop)
+        self.assertTrue(FakeEnv().dataset_id is data_prop)
+
+    def test_prop_descriptor(self):
+        from gcloud._testing import _Monkey
+        from gcloud.datastore import _implicit_environ
+
+        self.assertFalse(
+            'dataset_id' in _implicit_environ._DEFAULTS.__dict__)
+
+        DEFAULT = object()
+
+        def mock_default():
+            return DEFAULT
+
+        with _Monkey(_implicit_environ,
+                     _determine_default_dataset_id=mock_default):
+            lazy_loaded = _implicit_environ._DEFAULTS.dataset_id
+
+        self.assertEqual(lazy_loaded, DEFAULT)
+        self.assertTrue(
+            'dataset_id' in _implicit_environ._DEFAULTS.__dict__)
+
+
 class _AppIdentity(object):
 
     def __init__(self, app_id):

pylintrc_default

@@ -73,13 +73,18 @@ ignore =
 #                  identical implementation but different docstrings.
 # - star-args:  standard Python idioms for varargs:
 #                  ancestor = Query().filter(*order_props)
+# - method-hidden: Decorating a method in a class (e.g. in _DefaultsContainer)
+#                      @_lazy_property_deco
+#                      def dataset_id():
+#                          ...
 disable =
     maybe-no-member,
     no-member,
     protected-access,
     redefined-builtin,
     similarities,
     star-args,
+    method-hidden,
 
 
 [REPORTS]

regression/clear_datastore.py

@@ -17,9 +17,10 @@
 from six.moves import input
 
 from gcloud import datastore
+from gcloud.datastore import _implicit_environ
 
 
-datastore._DATASET_ENV_VAR_NAME = 'GCLOUD_TESTS_DATASET_ID'
+_implicit_environ._DATASET_ENV_VAR_NAME = 'GCLOUD_TESTS_DATASET_ID'
 datastore.set_defaults()
 
 

regression/datastore.py

@@ -17,12 +17,13 @@
 import unittest2
 
 from gcloud import datastore
+from gcloud.datastore import _implicit_environ
 # This assumes the command is being run via tox hence the
 # repository root is the current directory.
 from regression import populate_datastore
 
 
-datastore._DATASET_ENV_VAR_NAME = 'GCLOUD_TESTS_DATASET_ID'
+_implicit_environ._DATASET_ENV_VAR_NAME = 'GCLOUD_TESTS_DATASET_ID'
 datastore.set_defaults()
 
 

regression/populate_datastore.py

@@ -17,9 +17,10 @@
 from six.moves import zip
 
 from gcloud import datastore
+from gcloud.datastore import _implicit_environ
 
 
-datastore._DATASET_ENV_VAR_NAME = 'GCLOUD_TESTS_DATASET_ID'
+_implicit_environ._DATASET_ENV_VAR_NAME = 'GCLOUD_TESTS_DATASET_ID'
 datastore.set_defaults()