def list_instances(compute, project, zone):
    """Returns list of GCE instance resources for specified project

    :param compute: GCE compute resource object using googleapiclient.discovery
    :param project: string, GCE Project Id
    :param zone: string, GCE Name of zone
    :return: Instances information
    :rtype: list
    """
    result = compute.instances().list(project=project, zone=zone).execute()
    if 'items' not in result:
        return []
    return result['items']