BUG: Create empty dataframe with string dtype fails "data type not understood" (original) (raw)

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• I have confirmed this bug exists on the latest version of pandas.
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Code Sample, a copy-pastable example

In [1]: import pandas as pd

In [2]: pd.DataFrame({'a': ['b']}, dtype='string') Out[2]: a 0 b

In [3]: pd.DataFrame(columns=['a'], dtype='string')

TypeError Traceback (most recent call last) in ----> 1 pd.DataFrame(columns=['a'], dtype='string')

~/lib/miniconda/envs/xport/lib/python3.8/site-packages/pandas/core/frame.py in init(self, data, index, columns, dtype, copy) 433 ) 434 elif isinstance(data, dict): --> 435 mgr = init_dict(data, index, columns, dtype=dtype) 436 elif isinstance(data, ma.MaskedArray): 437 import numpy.ma.mrecords as mrecords

~/lib/miniconda/envs/xport/lib/python3.8/site-packages/pandas/core/internals/construction.py in init_dict(data, index, columns, dtype) 232 # no obvious "empty" int column 233 if missing.any() and not is_integer_dtype(dtype): --> 234 if dtype is None or np.issubdtype(dtype, np.flexible): 235 # GH#1783 236 nan_dtype = object

~/lib/miniconda/envs/xport/lib/python3.8/site-packages/numpy/core/numerictypes.py in issubdtype(arg1, arg2) 391 """ 392 if not issubclass_(arg1, generic): --> 393 arg1 = dtype(arg1).type 394 if not issubclass_(arg2, generic): 395 arg2_orig = arg2

TypeError: data type not understood

In [4]: pd.DataFrame(columns=['a'], dtype='float') Out[4]: Empty DataFrame Columns: [a] Index: []

Problem description

When trying to create an empty dataframe, one can specify some dtypes, like 'float', but dtype='string' raises TypeError: data type not understood.

Expected Output

Output of pd.show_versions()

INSTALLED VERSIONS

commit : None
python : 3.8.2.final.0
python-bits : 64
OS : Darwin
OS-release : 19.4.0
machine : x86_64
processor : i386
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.0.3
numpy : 1.18.2
pytz : 2019.3
dateutil : 2.8.1
pip : 20.0.2
setuptools : 46.1.3.post20200330
Cython : None
pytest : 5.4.1
hypothesis : None
sphinx : 3.0.1
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 2.11.2
IPython : 7.13.0
pandas_datareader: None
bs4 : None
bottleneck : None
fastparquet : None
gcsfs : None
lxml.etree : None
matplotlib : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pytables : None
pytest : 5.4.1
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
xlsxwriter : None
numba : None