BUG: invalid constrution of a Series with dtype=str

[jamesqo]

pd.Series('', dtype=str, index=range(1000))

throws a ValueError with the following message:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\james\AppData\Local\Programs\Python\Python36-32\lib\site-packages\pandas\core\series.py", line 266, in __init__
    data = SingleBlockManager(data, index, fastpath=True)
  File "C:\Users\james\AppData\Local\Programs\Python\Python36-32\lib\site-packages\pandas\core\internals.py", line 4402, in __init__
    fastpath=True)
  File "C:\Users\james\AppData\Local\Programs\Python\Python36-32\lib\site-packages\pandas\core\internals.py", line 2957, in make_block
    return klass(values, ndim=ndim, fastpath=fastpath, placement=placement)
  File "C:\Users\james\AppData\Local\Programs\Python\Python36-32\lib\site-packages\pandas\core\internals.py", line 2082, in __init__
    placement=placement, **kwargs)
  File "C:\Users\james\AppData\Local\Programs\Python\Python36-32\lib\site-packages\pandas\core\internals.py", line 111, in __init__
    raise ValueError('Wrong number of dimensions')
ValueError: Wrong number of dimensions

Would it be possible to fix the behavior to initialize the series to '' (or at least provide a clearer message)?

[ZhuBaohe]

pd.Series('', dtype=object, index=range(1000))
That's ok. String uses 'object' dtype.

[jreback]

this takes a different path in master. We pretty much treat str as object. So this is a construction bug.

In [4]: pd.Series('',  index=range(1000), dtype=str)
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-4-3bd08f17c610> in <module>()
----> 1 pd.Series('',  index=range(1000), dtype=str)

~/pandas/pandas/core/series.py in __init__(self, data, index, dtype, name, copy, fastpath)
    237             else:
    238                 data = _sanitize_array(data, index, dtype, copy,
--> 239                                        raise_cast_failure=True)
    240 
    241                 data = SingleBlockManager(data, index, fastpath=True)

~/pandas/pandas/core/series.py in _sanitize_array(data, index, dtype, copy, raise_cast_failure)
   3260         # GH 16605
   3261         # If not empty convert the data to dtype
-> 3262         if not isna(data).all():
   3263             data = np.array(data, dtype=dtype, copy=False)
   3264 

AttributeError: 'bool' object has no attribute 'all'

@jamesqo there is no reason to specify a dtype here as this will be inferred to object dtype anyhow (str as I said above is pretty much an alias for object dtype).

a PR to fix is welcome.

[jreback]

@jamesqo note that setting the string '' like this doesn't have much utilitiy. pandas has a full suite of string operations that are all NaN aware.