Dict override syntax to allow standard form: --cfg.dict.key val

CHANGELOG.rst

@@ -25,6 +25,8 @@ Added
 
 Fixed
 ^^^^^
+- Dict override syntax to allow standard form: --cfg.dict.key val (`#824
+  <https://github.com/omni-us/jsonargparse/pull/824>`__).
 - Evaluation of postponed annotations for dataclass inheritance across modules
   not working correctly (`#814
   <https://github.com/omni-us/jsonargparse/pull/814>`__).

jsonargparse/_typehints.py

@@ -919,7 +919,11 @@ def adapt_typehints(
     elif typehint_origin in mapping_origin_types:
         if isinstance(val, NestedArg):
             if isinstance(prev_val, dict):
-                val = {**prev_val, val.key: val.val}
+                if isinstance(val.key, str) and "." in val.key:
+                    key_prefix, key_suffix = val.key.split(".", 1)
+                    val = {**prev_val, key_prefix: {key_suffix: val.val}}
+                else:
+                    val = {**prev_val, val.key: val.val}
             else:
                 val = {val.key: val.val}
         elif isinstance(val, MappingProxyType):

jsonargparse_tests/test_typehints.py

@@ -1604,3 +1604,9 @@ def test_non_path_dump(parser):
     parser.add_argument("--data", type=Union[Path_fr, Dict[str, List[str]]])
     cfg = parser.parse_args(['--data={"key": ["value"]}'])
     assert json_or_yaml_load(parser.dump(cfg)) == {"data": {"key": ["value"]}}
+
+
+def test_dict_key_val_override(parser):
+    parser.add_argument("--data", type=dict[str, int])
+    data = parser.parse_args(["--data", '{"a": 0, "b": 1}', "--data.a", "100"]).data
+    assert (data["a"], data["b"]) == (100, 1)