'Get a list of keypairs.
:param user_id: Id of key-pairs owner (Admin only).
:param marker: Begin returning keypairs that appear later in the
keypair list than that represented by this keypair name
(optional).
:param limit: maximum number of keypairs to return (optional).'

@api_versions.wraps('2.35')
def list(self, user_id=None, marker=None, limit=None):

    params = {}
    if user_id:
        params['user_id'] = user_id
    if limit:
        params['limit'] = int(limit)
    if marker:
        params['marker'] = str(marker)
    query_string = utils.prepare_query_string(params)
    url = ('/%s%s' % (self.keypair_prefix, query_string))
    return self._list(url, 'keypairs')
