关于yield和yield from

def yield_func():
    for  _ in range(2):
        yield "12"


def yield_from_func():
    for  _ in range(2):
        yield from '12'
        
for a in yield_func():
    print(a)

for a in yield_from_func():
    print(a)
    
 '''
12
12
1
2
1
2
'''   
很明显就能看出来yield from就是把迭代器再进行一次迭代器生成可以想象成[12,12]变成[1,2,1,2]把里面第一次迭代后的每个值再进行一次迭代