def filter(self, **kwargs):
    for key, value in self.skills.iteritems():
        possible = False

        for arg in kwargs:
            if hasattr(self, "filter_" + arg):
                fun = getattr(self, "filter_" + arg)
                possible = fun(kwargs[arg])
            else:
                raise NameError("No such filter '%s'." % arg)

        if possible:
            yield key