In [1]: import pandas as pd In [2]: pd.Series([1,2,3]).sum(numeric_only=False) Out[2]: 6 In [3]: pd.Series([1,2,3]).sum(numeric_only=True) --------------------------------------------------------------------------- NotImplementedError Traceback (most recent call last) <ipython-input-3-2c46bd289e26> in <module>() ----> 1 pd.Series([1,2,3]).sum(numeric_only=True) /users/is/whughes/pyenvs/research/lib/python2.7/site-packages/pandas-0.16.2_ahl1-py2.7-linux-x86_64.egg/pandas/core/generic.pyc in stat_func(self, axis, skipna, level, numeric_only, **kwargs) 4253 skipna=skipna) 4254 return self._reduce(f, name, axis=axis, -> 4255 skipna=skipna, numeric_only=numeric_only) 4256 stat_func.__name__ = name 4257 return stat_func /users/is/whughes/pyenvs/research/lib/python2.7/site-packages/pandas-0.16.2_ahl1-py2.7-linux-x86_64.egg/pandas/core/series.pyc in _reduce(self, op, name, axis, skipna, numeric_only, filter_type, **kwds) 2081 if numeric_only: 2082 raise NotImplementedError( -> 2083 'Series.{0} does not implement numeric_only.'.format(name)) 2084 return op(delegate, skipna=skipna, **kwds) 2085 NotImplementedError: Series.sum does not implement numeric_only.