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BUG: Setting a pyarrow scalar value with the same type that expands the series changes the dtype into object #52235

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char101 opened this issue Mar 27, 2023 · 1 comment
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Arrow pyarrow functionality Bug Indexing Related to indexing on series/frames, not to indexes themselves setitem-with-expansion

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@char101
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char101 commented Mar 27, 2023

Pandas version checks

  • I have checked that this issue has not already been reported.
  • I have confirmed this bug exists on the latest version of pandas.
  • I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

s = pd.Series(datetime.now(), dtype='date32[pyarrow]')

s[1] = pa.scalar(datetime.now(), type='date32')

s
Out[60]: 
0    2023-03-27
1    2023-03-27
dtype: object
s = pd.Series([1,2,3], dtype='int32[pyarrow]')

s[3] = pa.scalar(4, type='int32')

s
Out[72]: 
0    1
1    2
2    3
3    4
dtype: object

Issue Description

Adding new pyarrow scalar value of the same type to a series changes its dtype into object. This make it impossible(?) to add to a date32 series without changing its dtype.

Expected Behavior

The series dtype should be kept.

Installed Versions

INSTALLED VERSIONS

commit : 5c15588
python : 3.11.1.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.19043
machine : AMD64
processor : Intel64 Family 6 Model 158 Stepping 9, GenuineIntel
byteorder : little
LC_ALL : None
LANG : None
LOCALE : English_Indonesia.1252

pandas : 2.1.0.dev0+284.g5c155883fd
numpy : 1.24.2
pytz : 2022.6
dateutil : 2.8.2
setuptools : 65.6.3
pip : 23.0.1
Cython : 0.29.32
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : 4.9.2
html5lib : 1.1
pymysql : None
psycopg2 : 2.9.5
jinja2 : 3.1.2
IPython : 8.6.0
pandas_datareader: None
bs4 : 4.11.1
bottleneck : 1.3.7
brotli : 1.0.9
fastparquet : None
fsspec : None
gcsfs : None
matplotlib : 3.7.1
numba : None
numexpr : 2.8.4
odfpy : None
openpyxl : 3.1.0
pandas_gbq : None
pyarrow : 11.0.0
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.10.1
snappy : None
sqlalchemy : 1.4.45
tables : None
tabulate : None
xarray : None
xlrd : 2.0.1
zstandard : None
tzdata : 2022.6
qtpy : 2.3.0
pyqt5 : None

@char101 char101 added Bug Needs Triage Issue that has not been reviewed by a pandas team member labels Mar 27, 2023
@char101 char101 changed the title BUG: Adding a pyarrow scalar value with the same type to a series series changes the dtype into object BUG: Adding a pyarrow scalar value with the same type to a series changes the dtype into object Mar 27, 2023
@mroeschke
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Thanks for the report. This is similar to #52056 and would be greatly aided if/when pyarrow is a required dependency in pandas

@mroeschke mroeschke changed the title BUG: Adding a pyarrow scalar value with the same type to a series changes the dtype into object BUG: Setting a pyarrow scalar value with the same type that expands the series changes the dtype into object Mar 27, 2023
@mroeschke mroeschke added Indexing Related to indexing on series/frames, not to indexes themselves Arrow pyarrow functionality and removed Needs Triage Issue that has not been reviewed by a pandas team member labels Mar 27, 2023
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Labels
Arrow pyarrow functionality Bug Indexing Related to indexing on series/frames, not to indexes themselves setitem-with-expansion
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