'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):

    try:
        domain = self.get_domain(domain_name, validate)
    except:
        domain = None
    return domain
