def add_target(target, catalogue, tag=""):
    """Add target to catalogue.

    Parameters
    ----------
    target: katpoint.Target object
    catalogue: katpoint.Catalogue object
    tag: str
        target tag

    Returns
    -------
    catalogue: katpoint.Catalogue

    """
    if catalogue.__contains__(target.name):
        if tag not in catalogue[target.name].tags:
            catalogue[target.name].tags.append(tag)
    else:
        catalogue.add(target, tags=tag)
    return catalogue