def __init__(self, message):
        if isinstance(message, list):
            self.messages = message
        else:
            assert isinstance(message, (basestring, Promise)), ("%s should be a string" % repr(message))
            self.messages = [message]
ValidationError can be passed a string or a list.
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-0.96/django/core/validators.py/ValidationError.__init__