cache = {}
def fun(s):
    ss = s.split('/')
    key = ss[0] + '/' + ss[1]
    if cache.has_key(key):
        return None
    else:
        cache[key] = 1
        return s

ls = ['02/27/1960', '07/21/2004', '08/13/2004', '09/12/2004', '02/27', '07/21', '08/13']

new_ls = filter(fun, ls)
print new_ls

cache = set()
def fun(s):
    ss = s.split('/')
    key = ss[0] + '/' + ss[1]
    if key in cache:
        return None
    else:
        cache.add(key)
        return s

ls = ['02/27/1960', '07/21/2004', '08/13/2004', '09/12/2004', '02/27', '07/21', '08/13']

new_ls = filter(fun, ls)
print new_ls