Fix from_dict() in the presence of optional datetime fields. (#329)

Author: emosenkis

src/betterproto/__init__.py

@@ -1180,8 +1180,8 @@ def from_dict(self: T, value: Dict[str, Any]) -> T:
             if value[key] is not None:
                 if meta.proto_type == TYPE_MESSAGE:
                     v = getattr(self, field_name)
+                    cls = self._betterproto.cls_by_field[field_name]
                     if isinstance(v, list):
-                        cls = self._betterproto.cls_by_field[field_name]
                         if cls == datetime:
                             v = [isoparse(item) for item in value[key]]
                         elif cls == timedelta:
@@ -1191,16 +1191,15 @@ def from_dict(self: T, value: Dict[str, Any]) -> T:
                             ]
                         else:
                             v = [cls().from_dict(item) for item in value[key]]
-                    elif isinstance(v, datetime):
+                    elif cls == datetime:
                         v = isoparse(value[key])
                         setattr(self, field_name, v)
-                    elif isinstance(v, timedelta):
+                    elif cls == timedelta:
                         v = timedelta(seconds=float(value[key][:-1]))
                         setattr(self, field_name, v)
                     elif meta.wraps:
                         setattr(self, field_name, value[key])
                     elif v is None:
-                        cls = self._betterproto.cls_by_field[field_name]
                         setattr(self, field_name, cls().from_dict(value[key]))
                     else:
                         # NOTE: `from_dict` mutates the underlying message, so no

tests/inputs/proto3_field_presence/proto3_field_presence.json

@@ -8,5 +8,6 @@
   },
   "test6": "B",
   "test7": "8589934592",
-  "test8": 2.5
+  "test8": 2.5,
+  "test9": "2022-01-24T12:12:42Z"
 }

tests/inputs/proto3_field_presence/proto3_field_presence.proto

@@ -1,5 +1,7 @@
 syntax = "proto3";
 
+import "google/protobuf/timestamp.proto";
+
 message InnerTest {
     string test = 1;
 }
@@ -13,6 +15,7 @@ message Test {
     optional TestEnum test6 = 6;
     optional uint64 test7 = 7;
     optional float test8 = 8;
+    optional google.protobuf.Timestamp test9 = 9;
 }
 
 enum TestEnum {

tests/inputs/proto3_field_presence/test_proto3_field_presence.py

@@ -35,4 +35,5 @@ def test_json(ref_json: str, obj_json: str) -> None:
         "test6": None,
         "test7": None,
         "test8": None,
+        "test9": None,
     }