Ok, looks like there's not much chance of agreeing on a syntax, so here's a decorator that covers the two use cases I know of:: * matching the signature of dict() and dict.update() * allowing arguments to have their names changed without worrying about backwards compatibility (e.g. ``def func(sequence)`` changing to ``def func(iterable)``) I've pasted the docstring and code below. The docstring should give you a pretty good idea of the functionality. Let me know if you have use cases this wouldn't cover. """ Functions declared ad @positional_only prohibit any arguments from being passed in as keyword arguments:: >>> @positional_only ... def foo(a, b=None, *args): ... return a, b, args ... >>> foo(1, 2, 3) (1, 2, (3,)) >>> foo(a=1, b=2) Traceback (most recent call last): ... TypeError: foo() does not allow keyword arguments Note that you can't use **kwargs arguments with a @positional_only function:: >>> @positional_only ... def foo(a, b=None, **kwargs): ... pass ... Traceback (most recent call last): ... TypeError: foo() may not have **kwargs If you need the functionality of **kwargs, you can request it by adding a final argument with the name _kwargs. The keyword arguments will be passed in (as a dict) through this argument:: >>> @positional_only ... def foo(a, b=None, _kwargs=None): ... return a, b, _kwargs ... >>> foo(1) (1, None, {}) >>> foo(1, 2) (1, 2, {}) >>> foo(1, bar=42, baz='spam') (1, None, {'baz': 'spam', 'bar': 42}) When your function is called with the wrong number of arguments, your callers will only see the number of arguments they expected. That is, argument counts will not include the _kwargs argument:: >>> foo() Traceback (most recent call last): ... TypeError: foo() takes at least 1 positional argument(s) (0 given) >>> foo(1, 2, 3) Traceback (most recent call last): ... TypeError: foo() takes at most 2 positional argument(s) (3 given) Note that unlike a normal **kwargs, using _kwargs in a @positional_only function causes *all* keyword arguments to be collected, even those with the same names as other function parameters:: >>> foo(1, a=42, b='spam') (1, None, {'a': 42, 'b': 'spam'}) >>> foo(1, _kwargs='this is just silly') (1, None, {'_kwargs': 'this is just silly'}) This is of course because all function parameters are considered to be positional only and therefore unnamed for the purposes of argument parsing. Note that you cannot use *args or **kwargs with the _kwargs argument:: >>> @positional_only ... def foo(a, b, _kwargs, *args): ... pass ... Traceback (most recent call last): ... TypeError: foo() may not have *args >>> @positional_only ... def foo(a, b, _kwargs, **kwargs): ... pass ... Traceback (most recent call last): ... TypeError: foo() may not have **kwargs """ import doctest import inspect import functools def positional_only(func): name = func.__name__ # don't allow **kwargs arg_names, args_name, kwargs_name, _ = inspect.getargspec(func) if kwargs_name is not None: raise TypeError('%s() may not have **kwargs' % name) # if no keyword arguments were requested, create a wrapper that # only accepts positional arguments (as *args) if not arg_names or arg_names[-1] != '_kwargs': # wrapper that raises an error for **kwargs def positional_wrapper(*args, **kwargs): if kwargs: msg = '%s() does not allow keyword arguments' raise TypeError(msg % name) return func(*args) # if keyword arguments were requested (through a final _kwargs), # create a wrapper that collects **kwargs and passes them in as # the final positional argument else: # don't allow *args if args_name is not None: msg = '%s() may not have *args' raise TypeError(msg % func.__name__) # determine defaults and expected argument counts defaults = func.func_defaults defaults = defaults and defaults[:-1] or [] n_expected = func.func_code.co_argcount - 1 min_expected = n_expected - len(defaults) def positional_wrapper(*args, **kwargs): # raise a TypeError for wrong number of arguments here # because func() needs to take the extra 'kwargs' # argument but the caller shouldn't know it arg_count_err = None if len(args) < min_expected: arg_count_err = 'at least %i' % min_expected if len(args) > n_expected: arg_count_err = 'at most %i' % n_expected if arg_count_err is not None: msg = '%s() takes %s positional argument(s) (%i given)' raise TypeError(msg % (name, arg_count_err, len(args))) # fill in defaults and add the final _kwargs argument, # then call the function with only positional arguments n_missing = n_expected - len(args) args += func.func_defaults[-n_missing - 1:-1] args += (kwargs,) return func(*args) # return the wrapped function functools.update_wrapper(positional_wrapper, func) return positional_wrapper if __name__ == '__main__': doctest.testmod() STeVe -- I'm not *in*-sane. Indeed, I am so far *out* of sane that you appear a tiny blip on the distant coast of sanity. --- Bucky Katt, Get Fuzzy