Python源码中输出结果问题，python源码输出结果,def func():

Python源码中输出结果问题，python源码输出结果,def func():

def func():    for x in range(3):        yield from (x for x in 'abc')def func2():    return ((yield from (x for x in 'abc') for x in range(3))for y in func():    print(y, end=',')  # output1print()for y in func2():    print(y, end=',')  # output2

output1:
a,b,c,a,b,c,a,b,c,
output2:
a,b,c,None,a,b,c,None,a,b,c,None,
请教下output2里的None怎么出来的？
原本以为两个输出应该是一样的。

def func2():    return ((yield from (x for x in 'abc')) for x in range(3))

def func3():    for x in range(3):        yield from (x for x in 'abc')        yield

编橙之家文章，