CALLBACKS = {
    'validate': lambda self, value: True,
    'render': lambda self, *args, **kwargs: '',
    'digest_key': None,
    'rendervalue': lambda self, *args, **kwargs: self.value,
    'initializer': None,
}

class Field:
    
    def wrap_callback(self, cb):
        if cb is None:
            return
        def func(*args, **kwargs):
            return cb(self, *args, **kwargs)
        return func
       
    def __init__(self, *, is_multiple=False, **callbacks):
        self.apply_filters = []
        for cb in CALLBACKS.keys():
            func = self.wrap_callback(
                callbacks.get(cb, CALLBACKS[cb])
            )
            if func is not None:
                setattr(self, cb, func)
        self.initializer = callbacks.get('initializer', lambda: '')
        #self.digest_key = callbacks.get('digest_key', None)
        self.error_msg = ''
        self.multiple = is_multiple
        self.options_map = {}
        self.is_valid = None

    @property
    def value(self):
        if not hasattr(self, '_value'):
            self._value = self.initializer()
        return self._value

    @value.setter
    def value(self, value):
        self._value = value

class ValidationError(RuntimeError):
    pass