diff --git a/Lib/functools.py b/Lib/functools.py index d5f43935e6cf79..b3428a4ca28ac0 100644 --- a/Lib/functools.py +++ b/Lib/functools.py @@ -817,8 +817,13 @@ def register(cls, func=None): return func def wrapper(*args, **kw): + if not args: + raise TypeError(f'{funcname} requires at least ' + '1 positional argument') + return dispatch(args[0].__class__)(*args, **kw) + funcname = getattr(func, '__name__', 'singledispatch function') registry[object] = func wrapper.register = register wrapper.dispatch = dispatch diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py index 7ffe000af04d2f..f9f96bac6d4ed2 100644 --- a/Lib/test/test_functools.py +++ b/Lib/test/test_functools.py @@ -2305,6 +2305,13 @@ def _(arg: typing.Iterable[str]): )) self.assertTrue(str(exc.exception).endswith(msg_suffix)) + def test_invalid_positional_argument(self): + @functools.singledispatch + def f(*args): + pass + msg = 'f requires at least 1 positional argument' + with self.assertRaisesRegexp(TypeError, msg): + f() if __name__ == '__main__': unittest.main() diff --git a/Misc/NEWS.d/next/Library/2018-07-08-18-49-41.bpo-33967.lhaAez.rst b/Misc/NEWS.d/next/Library/2018-07-08-18-49-41.bpo-33967.lhaAez.rst new file mode 100644 index 00000000000000..1e1e745789a4ee --- /dev/null +++ b/Misc/NEWS.d/next/Library/2018-07-08-18-49-41.bpo-33967.lhaAez.rst @@ -0,0 +1,2 @@ +functools.singledispatch now raises TypeError instead of IndexError when no +positional arguments are passed.