def complete_irf_name(irfs, site, exposure, azimuth=None):
    """
    Given a list of IRFs zenith angles, the chosen site, exposure and NBS, it returns the completed name of the IRFs
    :param irfs: <z20|z40|z60> str (list of str)
    :param site: <North|South> (str)
    :param exposure: <100s|0.5h|5h|50h> (str)
    :param azimuth: <average> (str or None)
    :return: list of completed IRF names
    """
    new_irfs = []
    for irf in irfs:
        if azimuth is None:
            new_irfs.append(site + '_z' + str(irf) + '_' + exposure)
        else:
            new_irfs.append(site + '_z' + str(irf) + '_' + str(azimuth) + '_' + exposure)
    return new_irfs