Deprecate version attribute

Change-Id: Ia9a136c2af44fdcafe02103bb163f8528fea900b
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

osc_placement/__init__.py

@@ -12,8 +12,19 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import warnings
+
 import pbr.version
 
 
-__version__ = pbr.version.VersionInfo(
-    'osc_placement').version_string()
+def __getattr__(name: str) -> str:
+    if name == '__version__':
+        warnings.warn(
+            "Accessing osc_placement.__version__ is deprecated and will be "
+            "removed in a future release. Use importlib.metadata instead: "
+            "importlib.metadata.version('osc-placement')",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+        return pbr.version.VersionInfo('osc_placement').version_string()
+    raise AttributeError(f"module 'osc_placement' has no attribute {name!r}")

releasenotes/notes/deprecate-version-attribute-150863e7fa273c8b.yaml

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