fix: remove trailing underscore in transcoding

google/api_core/path_template.py

@@ -308,9 +308,27 @@ def transcode(http_options, message=None, **request_kwargs):
             else:
                 try:
                     if message:
-                        request["body"] = getattr(leftovers, body)
-                        delete_field(leftovers, body)
+                        try:
+                            request["body"] = getattr(leftovers, body)
+                            delete_field(leftovers, body)
+                        except AttributeError as e:
+                            # gapic-generator-python appends underscores to field names
+                            # that collide with python keywords.
+                            # `_` is stripped away as it is not possible to
+                            # natively define a field with a trailing underscore in protobuf.
+                            # See related issue
+                            # https://github.com/googleapis/python-api-core/issues/227
+                            if hasattr(leftovers, body + "_"):
+                                request["body"] = getattr(leftovers, body + "_")
+                                delete_field(leftovers, body + "_")
+                            else:
+                                raise e
                     else:
+                        # gapic-generator-python appends underscores to field names
+                        # that collide with python keywords.
+                        leftovers = {
+                            key.rstrip("_"): val for key, val in leftovers.items()
+                        }
                         request["body"] = leftovers.pop(body)
                 except (KeyError, AttributeError):
                     continue

tests/unit/test_path_template.py

@@ -17,10 +17,21 @@
 import mock
 import pytest
 
+import proto
+
 from google.api import auth_pb2
 from google.api_core import path_template
 
 
+class Breakpoint(proto.Message):
+    name = proto.Field(proto.STRING, number=1)
+
+
+class SomeMessage(proto.Message):
+    breakpoint_ = proto.Field(Breakpoint, number=1)
+    debuggee_id = proto.Field(proto.STRING, number=2)
+
+
 @pytest.mark.parametrize(
     "tmpl, args, kwargs, expected_result",
     [
@@ -413,6 +424,25 @@ def test_transcode_with_wildcard(
             {"data": {"id": 1, "info": "some info"}, "foo": "bar"},
             ["post", "/v1/no/template", {"id": 1, "info": "some info"}, {"foo": "bar"}],
         ],
+        # Single field body with trailing underscore
+        [
+            [["post", "/v1/no/template", "data"]],
+            None,
+            {"data": {"id": 1, "info": "some info"}, "foo_": "bar"},
+            ["post", "/v1/no/template", {"id": 1, "info": "some info"}, {"foo": "bar"}],
+        ],
+        # Single field body with reserved keyword, using message where field name has trailing underscore
+        [
+            [["post", "/v1/no/template", "breakpoint"]],
+            SomeMessage(breakpoint_=Breakpoint(name="test"), debuggee_id="test")._pb,
+            {},
+            [
+                "post",
+                "/v1/no/template",
+                Breakpoint(name="test")._pb,
+                SomeMessage(debuggee_id="test")._pb,
+            ],
+        ],
         [
             [["post", "/v1/no/template", "oauth"]],
             auth_pb2.AuthenticationRule(