pandas 中的 astype(str) 引发 TypeError

Question

I have a simple dataframe produced an error stdcos.head() produce

  PartNo  Cost
0    180  8.95
1    213  0.32
2    215  2.77
3    216  3.02
4    218  1.37

stdcos.dtypes returns

PartNo     object
Cost      float64
dtype: object

Why in this case can raise a TypeError for stdcos['PartNo'].astype(str) ? Is it possible to have something to do with the weird PartNo dtype?

---

Sorry, this is the error message

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-48-791196d10a7a> in <module>
----> 1 stdcos['PartNo'].astype(str)

~\AppData\Local\Continuum\miniconda3\lib\site-packages\pandas\core\frame.py in __getitem__(self, key)
   2774                 if self.columns.nlevels > 1:
   2775                     return self._getitem_multilevel(key)
-> 2776                 return self._get_item_cache(key)
   2777 
   2778         # Do we have a slicer (on rows)?

~\AppData\Local\Continuum\miniconda3\lib\site-packages\pandas\core\generic.py in _get_item_cache(self, item)
   3584         res = cache.get(item)
   3585         if res is None:
-> 3586             values = self._data.get(item)
   3587             res = self._box_item_values(item, values)
   3588             cache[item] = res

~\AppData\Local\Continuum\miniconda3\lib\site-packages\pandas\core\internals\managers.py in get(self, item)
    966                         raise ValueError("cannot label index with a null key")
    967 
--> 968             return self.iget(loc)
    969         else:
    970 

~\AppData\Local\Continuum\miniconda3\lib\site-packages\pandas\core\internals\managers.py in iget(self, i)
    983         Otherwise return as a ndarray
    984         """
--> 985         block = self.blocks[self._blknos[i]]
    986         values = block.iget(self._blklocs[i])
    987 

TypeError: only integer scalar arrays can be converted to a scalar index

Answer 1

Thanks to @Juanpa.arrivillaga, I found the bug.

It comes from stdcos.columns = [['PartNo', 'Cost']]

So the column name is actually nested, but for some reason it display like a flat ones in jupyter notebook.

Changing it back to stdcos.columns = ['PartNo', 'Cost'] fixed the issue.