Python - 传递的项目数量错误2，位置意味着1

Question

我使用python为两个txt文件插入列＃34; amazon＆＃34;和＃34; yelp＆＃34; 通过以下功能，它可以正常工作。 这是代码：

for i in range(len(amazon)+1):
    a[i]='amazon'
amazon.insert(2,'label',a[i])

for i in range(len(yelp)+1):
    a[i]='yelp'
yelp.insert(2,'label',a[i])

但是，当我使用用户定义函数来调用它时，会发生一些错误。我可以知道这个功能是否有任何问题，因为我使用了相同的逻辑

def label(doc):
    for i in range(len(doc)):
        a[i]=doc
    return doc.insert(2,'label',a[i])

------------error msg:
ValueError                                Traceback (most recent call last)
<ipython-input-493-cc2a2cf79348> in <module>()
----> 1 label(imdb)

<ipython-input-492-d9cdd4df272b> in label(doc)
      2     for i in range(len(doc)):
      3         a[i]=doc
----> 4     return doc.insert(2,'label',a[i])

C:\Users\asus\Anaconda3\lib\site-packages\pandas\core\frame.py in insert(self, loc, column, value, allow_duplicates)
   2421         value = self._sanitize_column(column, value, broadcast=False)
   2422         self._data.insert(loc, column, value,
-> 2423                           allow_duplicates=allow_duplicates)
   2424 
   2425     def assign(self, **kwargs):

C:\Users\asus\Anaconda3\lib\site-packages\pandas\core\internals.py in insert(self, loc, item, value, allow_duplicates)
   3817 
   3818         block = make_block(values=value, ndim=self.ndim,
-> 3819                            placement=slice(loc, loc + 1))
   3820 
   3821         for blkno, count in _fast_count_smallints(self._blknos[loc:]):

C:\Users\asus\Anaconda3\lib\site-packages\pandas\core\internals.py in make_block(values, placement, klass, ndim, dtype, fastpath)
   2717                      placement=placement, dtype=dtype)
   2718 
-> 2719     return klass(values, ndim=ndim, fastpath=fastpath, placement=placement)
   2720 
   2721 # TODO: flexible with index=None and/or items=None

C:\Users\asus\Anaconda3\lib\site-packages\pandas\core\internals.py in __init__(self, values, ndim, fastpath, placement, **kwargs)
   1842 
   1843         super(ObjectBlock, self).__init__(values, ndim=ndim, fastpath=fastpath,
-> 1844                                           placement=placement, **kwargs)
   1845 
   1846     @property

C:\Users\asus\Anaconda3\lib\site-packages\pandas\core\internals.py in __init__(self, values, placement, ndim, fastpath)
    113             raise ValueError('Wrong number of items passed %d, placement '
    114                              'implies %d' % (len(self.values),
--> 115                                              len(self.mgr_locs)))
    116 
    117     @property

**ValueError: Wrong number of items passed 2, placement implies 1**