BUG: replace with 3 or more None values fails when copy_on_write is enabled

[timvink]

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

import pandas as pd
pd.DataFrame({'mycol' : ['one','two']}).replace({'mycol': {'<NA>': None, 'null': None, '': None}}) #  all good
pd.options.mode.copy_on_write = True
pd.DataFrame({'mycol' : ['one','two']}).replace({'mycol': {'<NA>': None, 'null': None, '': None}}) # error

Issue Description

When enabling copy_on_write, if you replace dictionary has 3 or more None values, it will return an error.

Interestingly, if you use two, it works:

import pandas as pd
pd.DataFrame({'mycol' : ['one','two']}).replace({'mycol': {'<NA>': None, 'null': None, '': None}}) #  all good
pd.options.mode.copy_on_write = True
pd.DataFrame({'mycol' : ['one','two']}).replace({'mycol': {'<NA>': None, 'null': None, '': None}}) # error
pd.DataFrame({'mycol' : ['one','two']}).replace({'mycol': {'<NA>': None, 'null': None}}) # works

Also, if you use pd.NA instead of None, it also works

Expected Behavior

Normal replacement, just like when copy_on_write is not enabled

Installed Versions

INSTALLED VERSIONS

commit : d9cdd2e
python : 3.10.14.final.0
python-bits : 64
OS : Linux
OS-release : 5.15.0-1064-azure
Version : #73~20.04.1-Ubuntu SMP Mon May 6 09:43:44 UTC 2024
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : C.UTF-8
LOCALE : en_US.UTF-8

pandas : 2.2.2
numpy : 2.1.1
pytz : 2024.1
dateutil : 2.9.0.post0
setuptools : 70.1.1
pip : 24.0
Cython : None
pytest : 8.2.2
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.4
IPython : 8.26.0
pandas_datareader : None
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.12.3
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : 2023.10.0
gcsfs : None
matplotlib : 3.9.2
numba : None
numexpr : None
odfpy : None
openpyxl : 3.1.5
pandas_gbq : None
pyarrow : None
pyreadstat : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : 1.14.1
sqlalchemy : 2.0.31
tables : None
tabulate : 0.9.0
xarray : None
xlrd : None
zstandard : None
tzdata : 2024.1
qtpy : None
pyqt5 : None

[rhshadrach]

Thanks for the report, confirmed on main. This also happens for string[python] and string[pyarrow]. I get the error

ValueError: <weakref at 0x78ca411edda0; to 'NumpyBlock' at 0x78ca411d64b0> is not in list

Further investigations and PRs to fix are welcome!

cc @phofl

[jorisvandenbossche]

I have a PR to fix this at #59807