Deprecate version attribute

Change-Id: Ibcfb2adb9e831ab613a8b9667a1c999e962d1e35
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

etcd3gw/__init__.py

@@ -10,6 +10,9 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+from typing import cast
+import warnings
+
 import pbr.version
 
 from etcd3gw.client import client
@@ -19,8 +22,6 @@ from etcd3gw.lock import Lock
 from etcd3gw import types
 from etcd3gw import utils
 
-__version__ = pbr.version.VersionInfo('etcd3gw').version_string()
-
 __all__ = (
     'Etcd3Client',
     'Lease',
@@ -29,3 +30,16 @@ __all__ = (
     'types',
     'utils',
 )
+
+
+def __getattr__(name: str) -> str:
+    if name == '__version__':
+        warnings.warn(
+            "Accessing etcd3gw.__version__ is deprecated and will be "
+            "removed in a future release. Use importlib.metadata instead: "
+            "importlib.metadata.version('etcd3gw')",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+        return cast(str, pbr.version.VersionInfo('etcd3gw').version_string())
+    raise AttributeError(f"module 'etcd3gw' has no attribute {name!r}")

releasenotes/notes/deprecate-version-attribute-11a5aee8633147a4.yaml

@@ -0,0 +1,6 @@
+---
+deprecations:
+  - |
+    The ``etcd3gw.__version__`` attribute has been deprecated for removal.
+    Prefer use of ``importlib.metadata`` to inspect version information for
+    installed packages.