列表嵌套如何实现提取其中元素并生成新列表？

问题简化后如下：现有嵌套列表a：
（a=[[['166'], ['166', '188'], ['166'],['180']], [['120'],['181'],['120', '151', '123']]]）

希望循环每个列表后生成如下新列表：（即依次提取嵌套列表内容）

a = [[['166'], ['166', '188'], ['166'], ['180']], [['120'], ['181'], ['120', '151', '123']]]

adiv = []

for i in a:
    xlen = 0
    for ik in i:
        if len(ik) > xlen:
            xlen = len(ik)

    for df in range(xlen):
        data = []
        for ix in i:
            if len(ix) == 1:
                data.append(ix[0])
            else:
                data.append(ix[0])
                ix.remove(ix[0])

        adiv.append(data)

print(adiv)


[['166', '166', '166', '180'], ['166', '188', '166', '180'], ['120', '181', '120'], ['120', '181', '151'], ['120', '181', '123']]