code: def lookup(self, domain_name, validate=True):
          
          try:
              domain = self.get_domain(domain_name, validate)
          except:
              domain = None
          return domain
docs: Lookup an existing SimpleDB domain. This differs from 
          :py:meth:`get_domain` in that ``None`` is returned if ``validate`` is
          ``True`` and no match was found (instead of raising an exception).
  
          :param str domain_name: The name of the domain to retrieve
          
          :param bool validate: If ``True``, a ``None`` value will be returned
              if the specified domain can't be found. If ``False``, a
              :py:class:`Domain <boto.sdb.domain.Domain>` object will be dumbly
              returned, regardless of whether it actually exists.
  
          :rtype: :class:`boto.sdb.domain.Domain` object or ``None``
          :return: The Domain object or ``None`` if the domain does not exist.