def _verify_sites(m, *site_list):
    """
    Checks that the monomer m contains all of the sites in site_list.

    Parameters
    ----------
    m : Monomer or MonomerPattern
        The monomer to check.
    site1, site2, ... : string
        One or more site names to check on m

    Returns
    -------
    True if m contains all sites; raises a ValueError otherwise.

    Raises
    ------
    ValueError
        If any of the sites are not found.

    """

    for site in site_list:
        if site not in m().monomer.sites:
            raise ValueError("Monomer '%s' must contain the site '%s'" %
                            (m().monomer.name, site))
    return True