实在不行就写个循环语句

func = lambda x: [y for l in x for y in func(l)] if type(x) is list else [x]
func(a)

自定义一个函数

def flat(a):
    l= []
    for i in a:
        if type(i) is list:
            for j in i:
                l.append(j)
        else:
            l.append(i)
    return(l)
flat(a)