Unicode not acceptable input for `usecols` kwarg in `read_csv()`

[PeterKucirek]

I caught this bug while updating from version 0.18.0 to 0.18.1. The kwarg usecols no longer accepts unicode column labels.

Example below:

from io import StringIO
import pandas as pd

s = u'''AAA,BBB,CCC,DDD
0.056674973,8,True,a
2.613230982,2,False,b
3.568935038,7,False,a
'''
buff = StringIO(s)
print pd.read_csv(buff, usecols=[u'AAA', u'BBB'])

>> ValueError: The elements of 'usecols' must either be all strings or all integers

I note that 0.18.1 introduced the requirement that usecols be all string or all ints. This makes sense but it looks like the implementation also throws away unicode strings.

[jreback]

makes sense, pull-requests welcome to fix

cc @gfyoung

[gfyoung]

@PeterKucirek: good catch! PR is definitely in order here. Shouldn't be too bad to implement.

[geraldstanje]

hi,

i get the same error:

ValueError: The elements of 'usecols' must either be all strings, all unicode, o
r all integers

i pandas with the following version:

C:\>pip install --upgrade pandas
Collecting pandas
  Downloading pandas-0.19.0-cp27-cp27m-win_amd64.whl (7.0MB)
    100% |################################| 7.1MB 193kB/s
Collecting pytz>=2011k (from pandas)
  Downloading pytz-2016.7-py2.py3-none-any.whl (480kB)
    100% |################################| 481kB 1.4MB/s
Collecting numpy>=1.7.0 (from pandas)
  Downloading numpy-1.11.2-cp27-none-win_amd64.whl (7.4MB)
    100% |################################| 7.4MB 184kB/s
Requirement already up-to-date: python-dateutil in c:\users\ger\appdata\loca
l\continuum\anaconda2\lib\site-packages (from pandas)
Requirement already up-to-date: six>=1.5 in c:\users\ger\appdata\local\conti
nuum\anaconda2\lib\site-packages (from python-dateutil->pandas)
Installing collected packages: pytz, numpy, pandas
  Found existing installation: pytz 2016.6.1
    DEPRECATION: Uninstalling a distutils installed project (pytz) has been depr
ecated and will be removed in a future version. This is due to the fact that uni
nstalling a distutils project will only partially uninstall the project.
    Uninstalling pytz-2016.6.1:
      Successfully uninstalled pytz-2016.6.1
  Found existing installation: numpy 1.11.1
    Uninstalling numpy-1.11.1:
      Successfully uninstalled numpy-1.11.1
  Found existing installation: pandas 0.18.1
    Uninstalling pandas-0.18.1:
      Successfully uninstalled pandas-0.18.1
Successfully installed numpy-1.11.2 pandas-0.19.0 pytz-2016.7

[gfyoung]

@geraldstanje : Can you show us the code snippet that broke?