Lazy load defaults

gcloud/datastore/__init__.py

@@ -46,10 +46,9 @@
   when race conditions may occur.
 """
 
-import os
-
 from gcloud import credentials
 from gcloud.datastore import _implicit_environ
+from gcloud.datastore._implicit_environ import set_default_dataset_id
 from gcloud.datastore.api import allocate_ids
 from gcloud.datastore.api import delete
 from gcloud.datastore.api import get
@@ -66,37 +65,6 @@
          'https://www.googleapis.com/auth/userinfo.email')
 """The scopes required for authenticating as a Cloud Datastore consumer."""
 
-_DATASET_ENV_VAR_NAME = 'GCLOUD_DATASET_ID'
-
-
-def set_default_dataset_id(dataset_id=None):
-    """Set default dataset ID either explicitly or implicitly as fall-back.
-
-    In implicit case, supports three cases. In order of precedence, the
-    implicit cases are:
-    - GCLOUD_DATASET_ID environment variable
-    - Google App Engine application ID
-    - Google Compute Engine project ID (from metadata server)
-
-    :type dataset_id: string
-    :param dataset_id: Optional. The dataset ID to use as default.
-
-    :raises: :class:`EnvironmentError` if no dataset ID was implied.
-    """
-    if dataset_id is None:
-        dataset_id = os.getenv(_DATASET_ENV_VAR_NAME)
-
-    if dataset_id is None:
-        dataset_id = _implicit_environ.app_engine_id()
-
-    if dataset_id is None:
-        dataset_id = _implicit_environ.compute_engine_id()
-
-    if dataset_id is not None:
-        _implicit_environ.DATASET_ID = dataset_id
-    else:
-        raise EnvironmentError('No dataset ID could be inferred.')
-
 
 def set_default_connection(connection=None):
     """Set default connection either explicitly or implicitly as fall-back.
@@ -105,7 +73,7 @@ def set_default_connection(connection=None):
     :param connection: A connection provided to be the default.
     """
     connection = connection or get_connection()
-    _implicit_environ.CONNECTION = connection
+    _implicit_environ.DEFAULT_ENVIRON.connection = connection
 
 
 def set_defaults(dataset_id=None, connection=None):

gcloud/datastore/_implicit_environ.py

@@ -12,12 +12,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-"""Module to provide implicit behavior based on enviroment.
+"""Module to provide implicit behavior based on environment.
 
 Acts as a mutable namespace to allow the datastore package to
-imply the current dataset ID and connection from the enviroment.
+imply the current dataset ID and connection from the environment.
 """
 
+import os
 import socket
 
 from six.moves.http_client import HTTPConnection  # pylint: disable=F0401
@@ -28,11 +29,34 @@
     app_identity = None
 
 
-DATASET_ID = None
-"""Module global to allow persistent implied dataset ID from enviroment."""
+_DATASET_ENV_VAR_NAME = 'GCLOUD_DATASET_ID'
 
-CONNECTION = None
-"""Module global to allow persistent implied connection from enviroment."""
+
+class _DatasetIDProperty(object):
+    """Descriptor for lazy loaded dataset ID."""
+
+    def __get__(self, obj, objtype):
+        if obj is None or objtype is not Environment:
+            return self
+
+        obj.dataset_id = get_default_dataset_id()
+        return obj.dataset_id
+
+
+class Environment(object):
+    """Container for environment settings.
+
+    :type dataset_id: string
+    :param dataset_id: Persistent implied dataset ID from environment.
+
+    :type connection: :class:`gcloud.datastore.connection.Connection`
+    :param connection: Persistent implied connection from environment.
+    """
+
+    dataset_id = _DatasetIDProperty()
+
+    def __init__(self):
+        self.connection = None
 
 
 def app_engine_id():
@@ -79,3 +103,55 @@ def compute_engine_id():
         pass
     finally:
         connection.close()
+
+
+def get_default_dataset_id(dataset_id=None):
+    """Get default dataset ID either explicitly or implicitly as fall-back.
+
+    In implicit case, supports three cases. In order of precedence, the
+    implicit cases are:
+    - GCLOUD_DATASET_ID environment variable
+    - Google App Engine application ID
+    - Google Compute Engine project ID (from metadata server)
+
+    :type dataset_id: string
+    :param dataset_id: Optional. The dataset ID to use as default.
+
+    :rtype: string or ``NoneType``
+    :returns: The inferred dataset or None.
+    """
+    if dataset_id is None:
+        dataset_id = os.getenv(_DATASET_ENV_VAR_NAME)
+
+    if dataset_id is None:
+        dataset_id = app_engine_id()
+
+    if dataset_id is None:
+        dataset_id = compute_engine_id()
+
+    return dataset_id
+
+
+def set_default_dataset_id(dataset_id=None):
+    """Set default dataset ID either explicitly or implicitly as fall-back.
+
+    In implicit case, supports three cases. In order of precedence, the
+    implicit cases are:
+    - GCLOUD_DATASET_ID environment variable
+    - Google App Engine application ID
+    - Google Compute Engine project ID (from metadata server)
+
+    :type dataset_id: string
+    :param dataset_id: Optional. The dataset ID to use as default.
+
+    :raises: :class:`EnvironmentError` if no dataset ID was implied.
+    """
+    dataset_id = get_default_dataset_id(dataset_id=dataset_id)
+
+    if dataset_id is not None:
+        DEFAULT_ENVIRON.dataset_id = dataset_id
+    else:
+        raise EnvironmentError('No dataset ID could be inferred.')
+
+
+DEFAULT_ENVIRON = Environment()

gcloud/datastore/api.py

@@ -18,7 +18,7 @@
 Query objects rather than via protobufs.
 """
 
-from gcloud.datastore import _implicit_environ
+from gcloud.datastore._implicit_environ import DEFAULT_ENVIRON
 from gcloud.datastore.batch import Batch
 from gcloud.datastore.transaction import Transaction
 from gcloud.datastore import helpers
@@ -57,9 +57,9 @@ def _require_dataset_id(dataset_id=None, first_key=None):
         return top.dataset_id
     if first_key is not None:
         return first_key.dataset_id
-    if _implicit_environ.DATASET_ID is None:
+    if DEFAULT_ENVIRON.dataset_id is None:
         raise EnvironmentError('Dataset ID could not be inferred.')
-    return _implicit_environ.DATASET_ID
+    return DEFAULT_ENVIRON.dataset_id
 
 
 def _require_connection(connection=None):
@@ -78,9 +78,9 @@ def _require_connection(connection=None):
         if top is not None:
             connection = top.connection
         else:
-            if _implicit_environ.CONNECTION is None:
+            if DEFAULT_ENVIRON.connection is None:
                 raise EnvironmentError('Connection could not be inferred.')
-            connection = _implicit_environ.CONNECTION
+            connection = DEFAULT_ENVIRON.connection
     return connection
 
 

gcloud/datastore/batch.py

@@ -15,7 +15,7 @@
 """Create / interact with a batch of updates / deletes."""
 
 from gcloud._localstack import _LocalStack
-from gcloud.datastore import _implicit_environ
+from gcloud.datastore._implicit_environ import DEFAULT_ENVIRON
 from gcloud.datastore import helpers
 from gcloud.datastore.key import _dataset_ids_equal
 from gcloud.datastore import _datastore_v1_pb2 as datastore_pb
@@ -70,8 +70,8 @@ def __init__(self, dataset_id=None, connection=None):
         :raises: :class:`ValueError` if either a connection or dataset ID
                  are not set.
         """
-        self._connection = connection or _implicit_environ.CONNECTION
-        self._dataset_id = dataset_id or _implicit_environ.DATASET_ID
+        self._connection = connection or DEFAULT_ENVIRON.connection
+        self._dataset_id = dataset_id or DEFAULT_ENVIRON.dataset_id
 
         if self._connection is None or self._dataset_id is None:
             raise ValueError('A batch must have a connection and '

gcloud/datastore/key.py

@@ -17,7 +17,7 @@
 import copy
 import six
 
-from gcloud.datastore import _implicit_environ
+from gcloud.datastore._implicit_environ import DEFAULT_ENVIRON
 from gcloud.datastore import _datastore_v1_pb2 as datastore_pb
 
 
@@ -400,10 +400,10 @@ def _validate_dataset_id(dataset_id, parent):
 
         if dataset_id is None:
 
-            if _implicit_environ.DATASET_ID is None:
+            if DEFAULT_ENVIRON.dataset_id is None:
                 raise ValueError("A Key must have a dataset ID set.")
 
-            dataset_id = _implicit_environ.DATASET_ID
+            dataset_id = DEFAULT_ENVIRON.dataset_id
 
     return dataset_id
 

gcloud/datastore/query.py

@@ -16,7 +16,7 @@
 
 import base64
 
-from gcloud.datastore import _implicit_environ
+from gcloud.datastore._implicit_environ import DEFAULT_ENVIRON
 from gcloud.datastore import _datastore_v1_pb2 as datastore_pb
 from gcloud.datastore import helpers
 from gcloud.datastore.key import Key
@@ -80,7 +80,7 @@ def __init__(self,
                  group_by=()):
 
         if dataset_id is None:
-            dataset_id = _implicit_environ.DATASET_ID
+            dataset_id = DEFAULT_ENVIRON.dataset_id
 
         if dataset_id is None:
             raise ValueError("No dataset ID supplied, and no default set.")
@@ -326,7 +326,7 @@ def fetch(self, limit=None, offset=0, start_cursor=None, end_cursor=None,
                  default has been set.
         """
         if connection is None:
-            connection = _implicit_environ.CONNECTION
+            connection = DEFAULT_ENVIRON.connection
 
         if connection is None:
             raise ValueError("No connection passed, and no default set")