BUG: .loc/.iloc/.at/iat setitem coerces a pd.Series to np.ndarray with object dtype · Issue #48933 · pandas-dev/pandas (original) (raw)

Pandas version checks

Reproducible Example

import pandas as pd

s1 = pd.Series(dtype='O', index=['a', 'b']) s1['a'] = pd.Series() s1.loc['b'] = pd.Series()

>> s1

a Series([], dtype: float64)

b [] <--------------- ?? wrong cast to np.ndarray

dtype: object

It works if the index is not specified

s2 = pd.Series(dtype='O', index=None) s2['a'] = pd.Series() s2.loc['b'] = pd.Series()

>> s2

a Series([], dtype: float64)

b Series([], dtype: float64)

dtype: object

Issue Description

A series with object dtype and a predefined index, cast items of type pd.Series to np.ndarray instead of preserving the series(-type). This apply to all accessors loc, iloc, at, iat and only works correctly with __setitem__..

Expected Behavior

The elements in a series of dtype object should not be casted in any case.

Installed Versions

INSTALLED VERSIONS

commit : 87cfe4e
python : 3.10.6.final.0
python-bits : 64
OS : Linux
OS-release : 5.15.0-48-generic
Version : #54-Ubuntu SMP Fri Aug 26 13:26:29 UTC 2022
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8
pandas : 1.5.0
numpy : 1.23.3
pytz : 2022.2.1
dateutil : 2.8.2
setuptools : 59.8.0
pip : 22.2.2
Cython : None
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : None
IPython : None
pandas_datareader: None
bs4 : None
bottleneck : None
brotli : None
fastparquet : None
fsspec : None
gcsfs : None
matplotlib : 3.6.0
numba : 0.56.2
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 9.0.0
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.9.1
snappy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
zstandard : None
tzdata : None