decorator.py

import inspect


def kwargs2args(f):
    argspec = inspect.getargspec(f)
    no_arg_only = len(argspec.defaults) - len(argspec.args)
    defaults = { argspec.args[no_arg_only+i]: d for i, d in enumerate(argspec.defaults)}
    def function(*args, **kwargs):  
        old_args = list(argspec.args)
        new_args = list()
        for arg in argspec.args:
            if arg not in kwargs:
                new_args.append(defaults[old_args.pop(0)])
        
        new_args = new_args + list(args)
        f(*new_args)
    function.argspec = argspec
    return function

@kwargs2args
def foo(x=1, y=1, *args): 
    print('x={}'.format(x), 'y={}'.format(y), args)

foo(1, 2) 
# ('x=1', 'y=1', (1, 2))