Strip trailing underscore from option names

src/argh/assembling.py

@@ -153,6 +153,9 @@ def infer_argspecs_from_function(
     )
 
     def _make_cli_arg_names_options(arg_name) -> Tuple[List[str], List[str]]:
+        # str.removesuffix() can be used here starting with Python 3.9
+        if arg_name.endswith("_"):
+            arg_name = arg_name[:-1]
         cliified_arg_name = arg_name.replace("_", "-")
         positionals = [cliified_arg_name]
         can_have_short_opt = arg_name[0] not in conflicting_opts
@@ -406,6 +409,13 @@ def set_default_command(
        If the parser was created with ``add_help=True`` (which is by default),
        option name ``-h`` is silently removed from any argument.
 
+    .. note::
+
+       Function argument names ending with an underscore will have a single
+       trailing underscore removed before being converted to CLI arguments.
+       This allows CLI arguments to have names that would otherwise clash with
+       a reserved word or shadow a builtin.
+
     """
     func_signature = inspect.signature(function)
 

src/argh/dispatching.py

@@ -373,7 +373,11 @@ def _flat_key(key):
         kwonly_names = [p.name for p in func_params if p.kind == p.KEYWORD_ONLY]
         varargs_names = [p.name for p in func_params if p.kind == p.VAR_POSITIONAL]
         positional_values = [values_by_arg_name[name] for name in positional_names]
-        values_by_name = dict((k, values_by_arg_name[k]) for k in kwonly_names)
+        # str.removesuffix() can be used from Python 3.9 onward
+        values_by_name = dict(
+            (k, values_by_arg_name[k[:-1] if k.endswith("_") else k])
+            for k in kwonly_names
+        )
 
         # *args
         if varargs_names:

tests/test_assembling.py

@@ -669,6 +669,24 @@ def cmd(foo_pos, bar_pos, *args, foo_kwonly="foo_kwonly", bar_kwonly):
     ]
 
 
+def test_trailing_underscore_in_argument_name():
+    "Stripping trailing underscores from named options"
+
+    def cmd(*, foo_="foo", bar_):
+        return (foo_, bar_)
+
+    parser = argh.ArghParser()
+    parser.add_argument = MagicMock()
+    parser.set_default_command(
+        cmd, name_mapping_policy=NameMappingPolicy.BY_NAME_IF_KWONLY
+    )
+    help_tmpl = argh.constants.DEFAULT_ARGUMENT_TEMPLATE
+    assert parser.add_argument.mock_calls == [
+        call("-f", "--foo", default="foo", type=str, help=help_tmpl),
+        call("-b", "--bar", required=True, help=help_tmpl),
+    ]
+
+
 @patch("argh.assembling.COMPLETION_ENABLED", True)
 def test_custom_argument_completer():
     "Issue #33: Enable custom per-argument shell completion"

tests/test_integration.py

@@ -594,6 +594,18 @@ def cmd(a_b):
     assert run(parser, "hello").out == "hello\n"
 
 
+def test_trailing_underscore_keys():
+    """One trailing underscore is ignored in function args."""
+
+    def cmd(*, a, b_, c__):
+        return f"a='{a}' b_='{b_}' c__='{c__}'"
+
+    parser = DebugArghParser()
+    parser.set_default_command(cmd)
+
+    assert run(parser, "--a x --b y --c- z").out == "a='x' b_='y' c__='z'\n"
+
+
 @mock.patch("argh.assembling.COMPLETION_ENABLED", True)
 def test_custom_argument_completer():
     "Issue #33: Enable custom per-argument shell completion"