Adding option to support keeping underscores in argument names

argparse_dataclass.py

@@ -334,7 +334,7 @@ def _add_dataclass_options(
         raise TypeError("cls must be a dataclass")
 
     for field in fields(options_class):
-        args = field.metadata.get("args", [f"--{field.name.replace('_', '-')}"])
+        args = field.metadata.get("args", [f"--{_get_arg_name(field)}"])
         positional = not args[0].startswith("-")
         kwargs = {
             "type": field.metadata.get("type", field.type),
@@ -448,7 +448,7 @@ def _handle_bool_type(field: Field, args: list, kwargs: dict):
         if field.default is True:
             kwargs["action"] = "store_false"
             if "args" not in field.metadata:
-                args[0] = f"--no-{field.name.replace('_', '-')}"
+                args[0] = f"--no-{_get_arg_name(field)}"
                 kwargs["dest"] = field.name
     elif field.metadata.get("required") is True:
         kwargs["action"] = BooleanOptionalAction
@@ -479,6 +479,12 @@ def _handle_argument_group(
     group.add_argument(*args, **kwargs)
 
 
+def _get_arg_name(field: Field):
+    if field.metadata.get("keep_underscores", False):
+        return field.name
+    return field.name.replace("_", "-")
+
+
 class ArgumentParser(argparse.ArgumentParser, Generic[OptionsType]):
     """Command line argument parser that derives its options from a dataclass.
 

tests/test_argumentparser.py

@@ -142,10 +142,6 @@ class Options:
         params = ArgumentParser(Options).parse_args(["--name", "john doe"])
         self.assertEqual(params.name, "John Doe")
 
-    @unittest.skipIf(
-        sys.version_info[:2] == (3, 6),
-        "Python 3.6 does not have datetime.fromisoformat()",
-    )
     def test_default_factory(self):
         @dataclass
         class Parameters:
@@ -302,6 +298,16 @@ class Options:
 
         self.assertRaises(ValueError, lambda: ArgumentParser(Options))
 
+    def test_keep_underscores(self):
+        @dataclass
+        class Args:
+            num_of_foo: int = field(metadata={"keep_underscores": True})
+            is_fun: bool = field(default=True, metadata={"keep_underscores": True})
+
+        params = ArgumentParser(Args).parse_args(["--num_of_foo=10", "--no-is_fun"])
+        self.assertEqual(10, params.num_of_foo)
+        self.assertFalse(params.is_fun)
+
 
 if __name__ == "__main__":
     unittest.main()