gistfile1.py

class Entity(object):

  errors = {}
  validators = {}

  def __init__(self, **kwargs):
    for name, value in kwargs.iteritems():
      try:
        if self._is_extra_property(name, value):
          self._extra_properties(name, value)
          continue
        self.__setattr__(name, value)
      except Exception, e:
        self.errors[name] = [e.message]

  def __setattr__(self, name, value):
    if name in self.validators.keys():
      for validator in self.validators[name]:
        try:
          validator(name, value).validate()
        except ModelValidationException, e:
          if not name in self.errors.keys():
            self.errors[name] = []
          self.errors[name].append(e.message)
    object.__setattr__(self, name, value)

class User(Entity, Base):

  validators = {'fieldname': [ValidatorBlah, ValidatorBleh]}
  #mi modelo sqlalchemy