Decorator allowing function to receive information on the parameters that were passed to it during call, regardless of whether they were positional or keyword-based.

explicit_checker.py

from functools import partial, wraps


def explicit_checker(func=None, names_arg='explicit_params'):
    """Decorator of function, allowing the function to receive names of attributes
    that were explicitly set (either positionally or as keyword arguments). The
    explicitly set arguments are received as set assigned to some keyword argument
    at function call (default name is "explicit_params").

    Example usage:
    >>> @explicit_checker
    def test(a=1, b=2, explicit_params=None):
        return a, b, explicit_params
    >>> test(1)
    (1, 2, set(['a']))
    >>> test(b=3)
    (1, 3, set(['b']))
    >>> @explicit_checker
    def test(a=1, explicit_params=None, *args, **kwargs):
        return a, args, kwargs, explicit_params
    >>> test(a=2, b=3)
    (2, (3,), {'b': 3}, set(['a', 'b']))

    :param func: function to be decorated
    :param names_arg: name of the argument to store set of names
    :return: decorated function
    """
    if func is None:
        # Decorator called not on function, return another decorator
        return partial(explicit_checker, names_arg=names_arg)

    varnames = func.func_code.co_varnames
    @wraps(func)
    def _wrapper(*args, **kwargs):
        kwargs[names_arg] = set(list(varnames[:len(args)]) + kwargs.keys())
        return func(*args, **kwargs)
    return _wrapper