'Register function mappings supplied by user'

def __init__(self, settings={}):

    CodePrinter.__init__(self, settings)
    self.known_functions = dict(known_functions)
    userfuncs = settings.get('user_functions', {})
    for (k, v) in userfuncs.items():
        if (not isinstance(v, list)):
            userfuncs[k] = [((lambda *x: True), v)]
            self.known_functions.update(userfuncs)
