IndexError raised on invalid csv file

Code Sample, a copy-pastable example if possible

$ python
Python 3.5.2 (default, Nov 17 2016, 17:05:23) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pandas
>>> pandas.__version__
'0.19.2'
>>> with open('/tmp/error.csv', 'w') as fp:
...     fp.write('+++123456789...\ncol1,col2,col3\n1,2,3\n')
... 
36
>>> pandas.DataFrame.from_csv('/tmp/error.csv')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/dominik/.local/lib/python3.5/site-packages/pandas/core/frame.py", line 1231, in from_csv
    infer_datetime_format=infer_datetime_format)
  File "/home/dominik/.local/lib/python3.5/site-packages/pandas/io/parsers.py", line 646, in parser_f
    return _read(filepath_or_buffer, kwds)
  File "/home/dominik/.local/lib/python3.5/site-packages/pandas/io/parsers.py", line 401, in _read
    data = parser.read()
  File "/home/dominik/.local/lib/python3.5/site-packages/pandas/io/parsers.py", line 939, in read
    ret = self._engine.read(nrows)
  File "/home/dominik/.local/lib/python3.5/site-packages/pandas/io/parsers.py", line 1550, in read
    values = data.pop(self.index_col[i])
IndexError: list index out of range

Problem description

When loading a file with the following content via pandas.DataFrame.from_csv an IndexError is raised from somewhere inside the parsers sub-package.

File content:

+++123456789...
col1,col2,col3
1,2,3

Expected Output

The expected behavior would be to raise a CParserError instead.

Output of pd.show_versions()

>>> pandas.show_versions()

INSTALLED VERSIONS

commit: None python: 3.5.2.final.0 python-bits: 64 OS: Linux OS-release: 4.4.0-78-generic machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8

pandas: 0.19.2 nose: 1.3.7 pip: 9.0.1 setuptools: 34.2.0 Cython: None numpy: 1.12.0 scipy: 0.18.1 statsmodels: None xarray: None IPython: 5.2.2 sphinx: None patsy: None dateutil: 2.6.0 pytz: 2016.10 blosc: None bottleneck: None tables: None numexpr: None matplotlib: 2.0.0 openpyxl: None xlrd: None xlwt: None xlsxwriter: 0.7.3 lxml: None bs4: 4.4.1 html5lib: 0.9999999 httplib2: 0.9.1 apiclient: None sqlalchemy: None pymysql: None psycopg2: None jinja2: 2.9.5 boto: None pandas_datareader: None

[jreback]

@Dominik1123

In [1]: data = '+++123456789...\ncol1,col2,col3\n1,2,3\n'

In [2]: pd.read_csv(StringIO(data))
Out[2]: 
         +++123456789...
col1 col2            col3
1    2                  3

In [3]: pd.read_csv(StringIO(data), index_col=0)
IndexError: list index out of range

In [4]: pd.DataFrame.from_csv(StringIO(data))
IndexError: list index out of range

you probably want this

In [9]: pd.read_csv(StringIO(data), skiprows=1)
Out[9]: 
   col1  col2  col3
0     1     2     3

.from_csv defaults to index_col=0, e.g. [4] (which pd.read_csv does not, see [2]).

So this is buggy, and doing something odd.

cc @gfyoung

[gfyoung]

Even so, we prefer to add a test for read_csv just in case. Can never have too many tests. 😉