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Reproducible Example

import pandas as pd from pandas.core.frame import Series print(pd.__version__) # '3.0.0.dev0+2752.ga885d67965' s: Series = pd.Series(["A-B", "C-D"]).convert_dtypes(dtype_backend="pyarrow") s.str.split("-") > # 0 ['A' 'B'] # 1 ['C' 'D'] s.str.split("-").str[0] # AttributeError: Can only use .str accessor with string values, not unknown-array.  # Did you mean: 'std'? s.str.split("-").list[0] > # 0 A # 1 C s.str.split("-").list[-1] > # pyarrow.lib.ArrowInvalid: Index -1 is out of bounds: should be greater than or  # equal to 0

Issue Description

I noticed that the latest nightly wheel (pandas 3.0.0.dev0+2752.ga885d67965) does not allow indexing into list elements produced by str.split() when using the pyarrow-backed string dtype.

s1 = Series(...).convert_dtype(dtype_backend="pyarrow")
s1.str.split().str[...] # attempting to access list items via str accessor
s1.str.split().list[-1] # negative index access via list accessor

Specifically, list element access via slice syntax (str[...]) and negative indexing (list[-1]) appear to be unsupported for pyarrow string arrays in the current nightly build.

The error message went like this:

1. AttributeError: Can only use .str accessor with string values, not unknown-array. Did you mean: 'std'? (str accessor)
2. pyarrow.lib.ArrowInvalid: Index -1 is out of bounds: should be greater than or equal to 0 (list accessor)

Expected Behavior

s = s.astype(pd.StringDtype())

s.str.split("-").str[-1]

0 B
1 D
dtype: object

Installed Versions