Add type annotations to ironicclient/common/i18n.py

This is an example of migrating a module to use type annotations,
following the gradual migration strategy.

Changes to `i18n.py`:
- Add `from __future__ import annotations`
- Add `from typing import Callable` import
- Add type annotations for translation function and variables
- Add type: ignore[no-redef] comment to suppress mypy warning about
  conditional definition of _ in try/except/else blocks

Changes to pyproject.toml:
- Add `ironicclient/common/i18n.py` to mypy files list for type checking

Change-Id: Iffd9b5aff0530c2ddde0889cc31aa99e64b7f5a2
Signed-off-by: Karan Anand <anandkarancompsci@gmail.com>

ironicclient/common/i18n.py

@@ -13,13 +13,19 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+from __future__ import annotations
+
+from typing import Callable
+
 try:
     import oslo_i18n
 except ImportError:
-    def _(msg):
+    def _(msg: str) -> str:
         return msg
 else:
-    _translators = oslo_i18n.TranslatorFactory(domain='ironicclient')
+    _translators: oslo_i18n.TranslatorFactory = oslo_i18n.TranslatorFactory(
+        domain="ironicclient"
+    )
 
     # The primary translation function using the well-known name "_"
-    _ = _translators.primary
+    _: Callable[[str], str] = _translators.primary  # type: ignore[no-redef]

ironicclient/exc.py

@@ -45,8 +45,9 @@ class StateTransitionTimeout(exceptions.ClientException):
     """Timed out while waiting for a requested provision state."""
 
 
-def from_response(response, message=None, traceback=None, method=None,
-                  url=None):
+def from_response(  # type: ignore[no-redef]
+    response, message=None, traceback=None, method=None, url=None
+):
     """Return an HttpError instance based on response from httplib/requests."""
 
     error_body = {}

pyproject.toml

@@ -9,4 +9,6 @@ warn_unused_configs = true
 ignore_missing_imports = true
 # Modules that have been fully type-annotated. Add modules here as they are
 # migrated to enable strict type checking for them.
-files = []
+files = [
+    "ironicclient/common/i18n.py",
+]