`passedargs` decorator allows the differentiation between a kwarg being passed a default value and no value being provided for a kwarg.

gistfile1.py

def passedargs(func):
    """
    This (unused) decorator adds a `passed` attribute to `func`, a dict whose
    keys are the parameter names of `func` and whose values are True if that
    particular argument was passed, and False if not. This is useful if you
    don't want to use a sentinel value to detect the lack of argument passing.
    This is bad, though, because it's harder to get rid of an argument than it
    is to change one.
    
    For whatever reason, I got it in my head I wanted to create an Object.get
    method, much like dict's, but instead of returning None when default isn't
    passed, an Exception would be raised.

    >>> @passedargs
    ... def f(test, default=None):
    ...     print f.passed
    ...
    >>> f('test')
    {'test': True, 'default': False}
    >>> f('test', None)
    {'test': True, 'default': True}
    """
    spec = inspect.getargspec(func)
    def inner(*args, **kwargs):
        inner.passed = {}
        i = 0
        for i in xrange(len(args)):
            inner.passed[spec.args[i]] = True
        for i in xrange(i+1, func.func_code.co_argcount):
            inner.passed[spec.args[i]] = spec.args[i] in kwargs
        return func(*args, **kwargs)
    return inner