parse arguments from dict (#4869)

* add parse_dict to parse arguments from dict

* add unit test for parse_dict

src/transformers/hf_argparser.py

@@ -158,3 +158,16 @@ class HfArgumentParser(ArgumentParser):
             obj = dtype(**inputs)
             outputs.append(obj)
         return (*outputs,)
+
+    def parse_dict(self, args: dict) -> Tuple[DataClass, ...]:
+        """
+        Alternative helper method that does not use `argparse` at all,
+        instead uses a dict and populating the dataclass types.
+        """
+        outputs = []
+        for dtype in self.dataclass_types:
+            keys = {f.name for f in dataclasses.fields(dtype)}
+            inputs = {k: v for k, v in args.items() if k in keys}
+            obj = dtype(**inputs)
+            outputs.append(obj)
+        return (*outputs,)