ValueError Traceback (most recent call last)
<ipython-input-672-9c619ea6d0ef> in <module>()
 14 print data_frame[cols].sum()
 15 print "---"
---> 16 print data_frame[cols].duplicated()
 17 
 18 
.../local/lib/python2.7/site-packages/pandas/util/decorators.pyc in wrapper(*args, **kwargs)
 89 else:
 90 kwargs[new_arg_name] = new_arg_value
---> 91 return func(*args, **kwargs)
 92 return wrapper
 93 return _deprecate_kwarg
.../local/lib/python2.7/site-packages/pandas/core/frame.pyc in duplicated(self, subset, keep)
 3100 
 3101 vals = (self[col].values for col in subset)
-> 3102 labels, shape = map(list, zip(*map(f, vals)))
 3103 
 3104 ids = get_group_index(labels, shape, sort=False, xnull=False)
ValueError: need more than 0 values to unpack

import pandas as pd
data_frame = pd.DataFrame({'a': [1]*5})
cols = ['a']
print data_frame[cols]
print "---"
print data_frame[cols].sum()
print "---"
print data_frame[cols].duplicated()
print "---"
cols = []
print data_frame[cols]
print "---"
print data_frame[cols].sum()
print "---"
print data_frame[cols].duplicated()

 a
0 1
1 1
2 1
3 1
4 1
---
a 5
dtype: int64
---
0 False
1 True
2 True
3 True
4 True
dtype: bool
---
Empty DataFrame
Columns: []
Index: [0, 1, 2, 3, 4]
---
Series([], dtype: float64)
---
0 False
1 True
2 True
3 True
4 True
dtype: bool

commit: None
python: 2.7.9.final.0
python-bits: 64
OS: Linux
OS-release: 3.19.0-58-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
pandas: 0.18.0
nose: 1.3.7
pip: 1.5.6
setuptools: 12.2
Cython: 0.23.4
numpy: 1.11.0
scipy: 0.16.1
statsmodels: None
xarray: None
IPython: 4.0.3
sphinx: None
patsy: 0.4.0
dateutil: 2.5.2
pytz: 2016.3
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: 0.7.6
lxml: None
bs4: 4.3.2
html5lib: 0.999
httplib2: 0.9
apiclient: None
sqlalchemy: None
pymysql: 0.6.6.None
psycopg2: None
jinja2: 2.8
boto: None