In [2]: pd.Series([[[2], [3], [4]]], index=['a'], dtype='object') Out[2]: a [[2], [3], [4]] dtype: object In [3]: pd.Series({'a' : [[2], [3], [4]]}, index=['a']) Out[3]: a [[2], [3], [4]] dtype: object In [4]: pd.Series({'a' : [[2], [3], [4]]}, index=['a'], dtype='object') --------------------------------------------------------------------------- ValueError Traceback (most recent call last) <ipython-input-4-03acef2498da> in <module>() ----> 1 pd.Series({'a' : [[2], [3], [4]]}, index=['a'], dtype='object') /home/nobackup/repo/pandas/pandas/core/series.py in __init__(self, data, index, dtype, name, copy, fastpath) 198 data = data._data 199 elif isinstance(data, dict): --> 200 data, index = self._init_dict(data, index, dtype) 201 dtype = None 202 copy = False /home/nobackup/repo/pandas/pandas/core/series.py in _init_dict(self, data, index, dtype) 275 276 # Input is now list-like, so rely on "standard" construction: --> 277 s = Series(values, index=keys, dtype=dtype) 278 279 # Now we just make sure the order is respected, if any /home/nobackup/repo/pandas/pandas/core/series.py in __init__(self, data, index, dtype, name, copy, fastpath) 241 raise_cast_failure=True) 242 --> 243 data = SingleBlockManager(data, index, fastpath=True) 244 245 generic.NDFrame.__init__(self, data, fastpath=True) /home/nobackup/repo/pandas/pandas/core/internals.py in __init__(self, block, axis, do_integrity_check, fastpath) 4426 if not isinstance(block, Block): 4427 block = make_block(block, placement=slice(0, len(axis)), ndim=1, -> 4428 fastpath=True) 4429 4430 self.blocks = [block] /home/nobackup/repo/pandas/pandas/core/internals.py in make_block(values, placement, klass, ndim, dtype, fastpath) 2962 placement=placement, dtype=dtype) 2963 -> 2964 return klass(values, ndim=ndim, fastpath=fastpath, placement=placement) 2965 2966 # TODO: flexible with index=None and/or items=None /home/nobackup/repo/pandas/pandas/core/internals.py in __init__(self, values, ndim, fastpath, placement, **kwargs) 2086 2087 super(ObjectBlock, self).__init__(values, ndim=ndim, fastpath=fastpath, -> 2088 placement=placement, **kwargs) 2089 2090 @property /home/nobackup/repo/pandas/pandas/core/internals.py in __init__(self, values, placement, ndim, fastpath) 110 ndim = values.ndim 111 elif values.ndim != ndim: --> 112 raise ValueError('Wrong number of dimensions') 113 self.ndim = ndim 114 ValueError: Wrong number of dimensions