REGR: ValueError: setting an array element with a sequence. when assigning an array.array using .loc

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Reproducible Example

import pandas as pd
import numpy as np
from array import array

df = pd.DataFrame({"A": [2,4,6,8]})

cenlon = array('d')
cenlon.append(45.345343)

# Problem
df.loc[0, 'CenLon'] = cenlon

# Solution 1
# df.loc[0, 'CenLon'] = np.array(cenlon)

# Solution 2
# df['CenLon'] = ''
# df.loc[0, 'CenLon'] = cenlon

Issue Description

If the Example above is running in a jupyter notebook, the notebook gets stuck and no error message is shown. The error message only appears in the console where the jupyter notebook is running. From the notebook inside it looks like the cell is still computing. The Example also includes two solutions to it, but a decent error message still would be nice.

Expected Behavior

It would be great if the error message would be displayed directly in the notebook or the provided datatype should be supported again. As background info: this datatype you will get when working with geopandas (https://geopandas.org/en/stable/index.html) and shaply (https://shapely.readthedocs.io/en/stable/manual.html) and you want to extract the centre coordinates of a geometry. Further, I think this was supported in a previous pandas version as the error just appeared on an older notebook (if wanted I could try to find out up to which version or you decide it is not supported anymore then I will let shaply and geopandas know).

Installed Versions

INSTALLED VERSIONS ------------------ commit : 06d230151e6f18fdb8139d09abf539867a8cd481 python : 3.9.10.final.0 python-bits : 64 OS : Linux OS-release : 5.14.0-1024-oem Version : #26-Ubuntu SMP Thu Feb 17 14:35:50 UTC 2022 machine : x86_64 processor : x86_64 byteorder : little LC_ALL : None LANG : en_US.UTF-8 LOCALE : en_US.UTF-8

pandas : 1.4.1 numpy : 1.22.3 pytz : 2021.3 dateutil : 2.8.2 pip : 22.0.4 setuptools : 59.8.0 Cython : 0.29.28 pytest : 7.0.1 hypothesis : None sphinx : None blosc : None feather : None xlsxwriter : None lxml.etree : None html5lib : None pymysql : None psycopg2 : None jinja2 : 3.0.3 IPython : 8.1.1 pandas_datareader: None bs4 : None bottleneck : None fastparquet : None fsspec : 2022.02.0 gcsfs : None matplotlib : 3.5.1 numba : None numexpr : 2.8.0 odfpy : None openpyxl : None pandas_gbq : None pyarrow : None pyreadstat : None pyxlsb : None s3fs : None scipy : 1.8.0 sqlalchemy : None tables : 3.7.0 tabulate : None xarray : 2022.3.0 xlrd : None xlwt : None zstandard : None

[jorisvandenbossche]

BTW, the fact that a notebook is hanging and you see that long traceback in IPython, that was a bug in IPython that should be fixed in the latest version (https://github.com/ipython/ipython/issues/12467)

That still leaves the regression or behaviour change in pandas. I started investigating this and have an PR at https://github.com/pandas-dev/pandas/pull/48057

[simonjayhawkins]

moving to 1.4.4