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Reproducible Example

import pandas as pd
pd.options.mode.copy_on_write = True

idx = pd.Index(['a', 'b', 'c'], dtype="string[pyarrow]")
pd.Series(idx).replace({"z": "b", "a": "d"})

Issue Description

The above code raises the following issue: NotImplementedError: eq not implemented for <class 'pandas.core.internals.blocks.ExtensionBlock'>

Expected Behavior

The code should run without raising any error as it does without the CoW clause, shouldn't it?

Installed Versions

INSTALLED VERSIONS ------------------ commit : 2cc37625532045f4ac55b27176454bbbc9baf213 python : 3.12.5 python-bits : 64 OS : Windows OS-release : 11 Version : 10.0.26100 machine : AMD64 processor : Intel64 Family 6 Model 154 Stepping 3, GenuineIntel byteorder : little LC_ALL : None LANG : en LOCALE : English_United Kingdom.1252 pandas : 2.3.0 numpy : 2.1.3 pytz : 2024.1 dateutil : 2.9.0 pip : 24.2 Cython : None sphinx : None IPython : 8.32.0 adbc-driver-postgresql: None adbc-driver-sqlite : None bs4 : 4.12.3 blosc : None bottleneck : None dataframe-api-compat : None fastparquet : None fsspec : None html5lib : 1.1 hypothesis : None gcsfs : None jinja2 : 3.1.4 lxml.etree : 5.3.0 matplotlib : 3.9.2 numba : None numexpr : None odfpy : None openpyxl : 3.1.5 pandas_gbq : None psycopg2 : 2.9.9 pymysql : None pyarrow : 17.0.0 pyreadstat : None pytest : None python-calamine : None pyxlsb : None s3fs : None scipy : 1.14.0 sqlalchemy : 2.0.35 tables : None tabulate : None xarray : None xlrd : 2.0.1 xlsxwriter : 3.2.0 zstandard : 0.23.0 tzdata : 2024.1 qtpy : None pyqt5 : None

Comment From: jbrockmendel

cc @phofl

Comment From: rhshadrach

I haven't run a bisection, but this looks likely to be due to https://github.com/pandas-dev/pandas/pull/52008. Having the weakref to an Index looks like it could be a footgun due to equality comparisons, but we can at least work around here by replacing

https://github.com/pandas-dev/pandas/blob/e72c8a1e0ad421c1b8a7b918d995f24bed595cc3/pandas/core/internals/blocks.py#L871-L873

with something like

idx = next(iter(k for k, e in enumerate(b.refs.referenced_blocks) if e() is b))
b.refs.referenced_blocks.pop(idx)

Not familiar with how refs to index objects are handled elsewhere.