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.

def lookup(self, domain_name, validate=True):
        """
        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.
        """
        try:
            domain = self.get_domain(domain_name, validate)
        except:
            domain = None
        return domain