def underline_to_camel(underline_format):  
    word_set = underline_format.split('_')
    if len(word_set) == 1:
        return underline_format

    camel_format = ''  
    for i in range(len(word_set)):  
        if i == 0:
            continue
        word_set[i] = word_set[i].capitalize()  
    return ''.join(word_set)  

print underline_to_camel(‘aaa’)
print underline_to_camel(‘aaa_bbb’)
print underline_to_camel(‘aaa_bbb_ccc’)