'List the grants for a specified key.
:type key_id: string
:param key_id: Unique identifier of the key. This can be an ARN, an
alias, or a globally unique identifier.
:type limit: integer
:param limit: Specify this parameter only when paginating results to
indicate the maximum number of grants you want listed in the
response. If there are additional grants beyond the maximum you
specify, the `Truncated` response element will be set to `true.`
:type marker: string
:param marker: Use this parameter only when paginating results, and
only in a subsequent request after you\'ve received a response where
the results are truncated. Set it to the value of the `NextMarker`
in the response you just received.'

def list_grants(self, key_id, limit=None, marker=None):

    params = {'KeyId': key_id}
    if (limit is not None):
        params['Limit'] = limit
    if (marker is not None):
        params['Marker'] = marker
    return self.make_request(action='ListGrants', body=json.dumps(params))
