BUG: df.loc astype type change on specific row not working

[ganbaaelmer]

Pandas version checks

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Reproducible Example

df.loc[index, 'column_name'].astype(str)

Issue Description

astype(str) not working

Expected Behavior

object to str not working. dtype still object

Installed Versions

INSTALLED VERSIONS ------------------ commit : d9cdd2ee5a58015ef6f4d15c7226110c9aab8140 python : 3.12.4.final.0 python-bits : 64 OS : Windows OS-release : 11 Version : 10.0.22631 machine : AMD64 processor : Intel64 Family 6 Model 151 Stepping 5, GenuineIntel byteorder : little LC_ALL : None LANG : None LOCALE : English_United States.1252 pandas : 2.2.2 numpy : 1.26.4 pytz : 2024.1 dateutil : 2.9.0.post0 setuptools : 69.5.1 pip : 24.0 Cython : None pytest : 7.4.4 hypothesis : None sphinx : 7.3.7 blosc : None feather : None xlsxwriter : None lxml.etree : 5.2.1 html5lib : None pymysql : None psycopg2 : None jinja2 : 3.1.4 IPython : 8.25.0 pandas_datareader : None adbc-driver-postgresql: None adbc-driver-sqlite : None bs4 : 4.12.3 bottleneck : 1.3.7 dataframe-api-compat : None fastparquet : None fsspec : 2024.3.1 gcsfs : None matplotlib : 3.8.4 numba : 0.59.1 numexpr : 2.8.7 odfpy : None openpyxl : 3.1.2 pandas_gbq : None pyarrow : 14.0.2 pyreadstat : None python-calamine : None pyxlsb : None s3fs : 2024.3.1 scipy : 1.13.1 sqlalchemy : 2.0.30 tables : 3.9.2 tabulate : 0.9.0 xarray : 2023.6.0 xlrd : None zstandard : 0.22.0 tzdata : 2023.3 qtpy : 2.4.1 pyqt5 : None

[rhshadrach]

Thanks for the report. Currently str uses NumPy object dtypes. But this is an area of pandas that is under active development and will change in the future. See https://pandas.pydata.org/pdeps/0014-string-dtype.html for more details. You can enable it by using pd.options.future.infer_string = True:

pd.options.future.infer_string = True
ser = pd.Series(["a", "b", None])
print(ser.astype("str").dtype)
# str

@jorisvandenbossche - I'm seeing the following:

pd.options.future.infer_string = True
ser = pd.Series(["a", "b", None])
print(ser.astype(str).dtype)
# object

Is that expected to be object dtype?

[ganbaaelmer]

i think this one is working

pd.options.future.infer_string = True
df[column_A] = df[column_A].astype('str')