Groupby doesn't accept level=[0] for Index.

[starhel]

Today I've found weird behaviour of level parameter of groupby. I need to groupby two dataframes by index and this code is working as long as I'm using Multiindex.

index1 = pandas.Index([1,2,3,4,5])
index2 = pandas.Index([1,2,3,4,5])
first = pandas.DataFrame({'a':[1,2,3,4,5]}, index=index1)
second = df2 = pandas.DataFrame({'a':[2,3,4,5,6]}, index=index2)
pandas.concat([first, second]).groupby(level=range(first.index.nlevels)).min()

Unfortunately when I'm using simple Index I get:

ValueError: level > 0 only valid with MultiIndex

In other way if I passed 0 instead of [0], everything is working properly. It's weird and cause that it's hard to write reusable code.

INSTALLED VERSIONS

commit: None
python: 2.7.12.final.0
python-bits: 64
OS: Linux
OS-release: 4.2.0-42-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF8

pandas: 0.18.1
nose: 1.3.7
pip: 8.1.2
setuptools: 20.3
Cython: None
numpy: 1.11.1
scipy: None
statsmodels: None
xarray: None
IPython: 4.2.0
sphinx: None
patsy: None
dateutil: 2.4.1
pytz: 2016.4
blosc: None
bottleneck: 1.1.0
tables: 3.2.2
numexpr: 2.6.0
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: 1.1.2
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.13
pymysql: None
psycopg2: None
jinja2: None
boto: None
pandas_datareader: None

[sinhrks]

Using range as level may work but not intended. It doesn't work PY3 at least.

[jreback]

I suppose this is legit, as [0] de-facto is equivalent to a scalar.

[sinhrks]

ok, then the fix should include the support of range in py3.

[sinhrks]

ah sorry you refer to one length list, not range, @jreback?

[jreback]

yes @sinhrks we don't accept non-list-likes anywhere (meaning range) for things like this. They must be a list/tuple/array (or scalar in this case)

[starhel]

@sinhrks Sorry for the confusion. In python2 range returns list and I totally forgot about the change in py3.

[agraboso]

In Python 3 range is an iterable — equivalent to Python 2's xrange. It fits the is_list_like definition, so my PR does accept them.