def ORFadvisor(DNA):
    if DNA[0:3] != 'ATG':
       return 'The first three bases are not ATG'
    # if DNA[-3:] != 'TAG' and DNA[-3:] != 'TGA' and DNA[-3:] != 'TAA':
    #    return 'The last three bases are not a stop codon'
    if DNA[-3:] not in ['TGA', 'TAG', 'TAA']:
       return 'The last three bases are not a stop codon'
    if len(DNA) % 3 != 0:
       return 'The string is not of the correct length'
    return 'This is an ORF'