def singers ():
    print 'This program rates singers.'
    excellentList = ['River Cuomo', 'Billy Joel', 'Bruce Springsteen', 'David Bowie'];
    goodList = ['Corey Taylor', 'Katy Perry'];
    sosoList = ['Drake'];
    singersList = excellentList + goodList + sosoList;
    print 'List of all Singers: ', singersList;

    while (True):
        singer = raw_input('Enter singer name (unquoted): ');
        if (singer in excellentList): rating = Excellent;
        elif (singer in goodList): rating = Good;
        elif (singer in sosoList): rating = So-so;
        else: rating = unknown;
        print 'Singer', singer, 'Rating:', rating;
        ans = inputYesNo('Process more? [Yes/No]: ');
        if (ans == 'No'): break;
    print 'So long...';

# Input valid answer for a Yes/No question:
def inputYesNo(prompt):
    response = raw_input(prompt);
    while (response != 'Yes' and response != 'No'):
        print 'Invalid response: ', response;
        response = raw_input(prompt);
    return response;