[traner] fix --lr_scheduler_type choices (#9800)

* fix --lr_scheduler_type choices

* rewrite to fix for all enum-based cl args

* cleanup

* adjust test

* style

* Proposal that should work

* Remove needless code

* Fix test

Co-authored-by: Sylvain Gugger <sylvain.gugger@gmail.com>

tests/test_hf_argparser.py

@@ -55,7 +55,10 @@ class BasicEnum(Enum):
 
 @dataclass
 class EnumExample:
-    foo: BasicEnum = BasicEnum.toto
+    foo: BasicEnum = "toto"
+
+    def __post_init__(self):
+        self.foo = BasicEnum(self.foo)
 
 
 @dataclass
@@ -133,14 +136,18 @@ class HfArgumentParserTest(unittest.TestCase):
         parser = HfArgumentParser(EnumExample)
 
         expected = argparse.ArgumentParser()
-        expected.add_argument("--foo", default=BasicEnum.toto, choices=list(BasicEnum), type=BasicEnum)
+        expected.add_argument("--foo", default="toto", choices=["titi", "toto"], type=str)
         self.argparsersEqual(parser, expected)
 
         args = parser.parse_args([])
-        self.assertEqual(args.foo, BasicEnum.toto)
+        self.assertEqual(args.foo, "toto")
+        enum_ex = parser.parse_args_into_dataclasses([])[0]
+        self.assertEqual(enum_ex.foo, BasicEnum.toto)
 
         args = parser.parse_args(["--foo", "titi"])
-        self.assertEqual(args.foo, BasicEnum.titi)
+        self.assertEqual(args.foo, "titi")
+        enum_ex = parser.parse_args_into_dataclasses(["--foo", "titi"])[0]
+        self.assertEqual(enum_ex.foo, BasicEnum.titi)
 
     def test_with_list(self):
         parser = HfArgumentParser(ListExample)