operator如何获得正确的值

Question

def start_when(iterable,p):
    s = ''
    a = ''
    x = iter(iterable)
    for x in list(iterable):
        a = a + x
    try:
        while True:
            y = next(x)
            if p(y) == True:
                s = s + a[a.index(y):]
    except StopIteration:
        pass
    return s

start_when生成器将iterable和谓词作为参数：它从iterable中生成每个值，从谓词返回True的第一个值开始 例如：

for i in start_when('combustible', lambda x : x >= 'q’):
    print(i,end='')

它打印＆＃39; ustible＆＃39;

它给出了以下错误：

    21 *Error: ''.join([str(v) for v in start_when('abcdefghijk', lambda x : x >='d')]) raised exception TypeError: 'str' object is not an iterator
    22 *Error: ''.join([str(v) for v in start_when(hide('abcdefghijk'), lambda x : x >='d')]) raised exception TypeError: 'str' object is not an iterator
    23 *Error: ''.join([str(v) for v in start_when(hide('abcdefghijk'), lambda x : x >'f')]) raised exception TypeError: 'str' object is not an iterator

有人可以帮我解决吗？非常感谢