def __repr__(self):
        return "<NamedRequirements({}{})>".format(
            self.name,
            ", filename='{}'".format(self.filename.name) if self.filename
            else "")
def serialize(self, value, display=False):
        lookup = {v: k for k, v in self.levels.items()}
        if value in lookup:
            return encode(lookup[value])
        return ""