code: def convert(self, value, param, ctx):
          
          rxp = '^[^@]+?@[-.a-z0-9]+$'
          regex = re.compile(rxp, re.I)
          try:
              if regex.match(value):
                  value = value.split("@")
                  return value
              else:
                  self.fail('%s is not a valid email address' % value, param,
                            ctx)
          except ValueError:
              self.fail('%s is not a valid email address' % value, param, ctx)
docs: Validate value using regexp.