Python validators. The general form comes exactly from Python in Practice: Create Better Programs Using Concurrency, Libraries, and Patterns Very useful: http://my.safaribooksonline.com/book/programming/python/9780133373271/2dot-structural-design-patterns-in-python/ch02lev1sec4_html

validation.py

def ensure(name, validate, doc=None):
    def decorator(Class):
        privateName = "__" + name
        def getter(self):
            return getattr(self, privateName)
        def setter(self, value):
            validate(name, value)
            setattr(self, privateName, value)
        setattr(Class, name, property(getter, setter, doc=doc))
        return Class
    return decorator

def is_str(name, value):
    if not isinstance(value, str):
        raise ValueError("{} must be a string".format(name))

def x_is_in_array(vallist):
    def x_is_in_array(name,value):
        if value not in vallist:
            raise ValueError("For field {} : {} is not in {}".format(name,value,vallist))
    return x_is_in_array

@ensure('strthing',is_str)
@ensure('arraything',x_is_in_array(ARRAYNAME))
class MEOW(object)
   pass