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BUG: testing.assert_frame_equal unhelpful error message for string[pyarrow] #54190

Open
2 of 3 tasks
Tracked by #54792
randolf-scholz opened this issue Jul 19, 2023 · 0 comments
Open
2 of 3 tasks
Tracked by #54792

BUG: testing.assert_frame_equal unhelpful error message for string[pyarrow] #54190

randolf-scholz opened this issue Jul 19, 2023 · 0 comments
Labels
Arrow pyarrow functionality Bug IO Parquet parquet, feather Strings String extension data type and string data
Milestone
2.3

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@randolf-scholz
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randolf-scholz commented Jul 19, 2023 •
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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

df = (
    pd.DataFrame({"a": [1, 2, 3], "b": [1.0, 2.0, None], "c": [None, "x", "y"]})
    .astype({"a": "int64[pyarrow]", "b": "float64[pyarrow]", "c": "string[pyarrow]"})
    .set_index("a")
)
df.to_parquet("demo.parquet")
df2 = pd.read_parquet("demo.parquet", dtype_backend="pyarrow")
pd.testing.assert_frame_equal(df, df2)

results in the error message

AssertionError: Attributes of DataFrame.iloc[:, 1] (column name="c") are different

Attribute "dtype" are different
[left]:  string[pyarrow]
[right]: string[pyarrow]

Issue Description

The problem is that

print(type(df.dtypes[-1]))   # string_.StringDtype'
print(type(df2.dtypes[-1]))  # arrow.dtype.ArrowDtype

have the same string representation

import pyarrow as pa
import pandas as pd

print(repr(pd.ArrowDtype(pa.string())))  # string[pyarrow]
print(repr(pd.StringDtype("pyarrow")))  # string[pyarrow]

Expected Behavior

  1. StringDtype("pyarrow") and ArrowDtype("string") need different repr
  2. testing.assert_frame_equal should consider printing not just repr(dtype), but also repr(type(dtype)).
  3. pd.read_parquet should round trip both index and column dtypes #

Additional context

As per https://pandas.pydata.org/docs/user_guide/pyarrow.html

The string alias "string[pyarrow]" maps to pd.StringDtype("pyarrow") which is not equivalent to specifying dtype=pd.ArrowDtype(pa.string()). Generally, operations on the data will behave similarly except pd.StringDtype("pyarrow") can return NumPy-backed nullable types while pd.ArrowDtype(pa.string()) will return ArrowDtype.

Installed Versions

INSTALLED VERSIONS
------------------
commit           : 0f437949513225922d851e9581723d82120684a6
python           : 3.11.3.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.19.0-46-generic
Version          : #47~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Wed Jun 21 15:35:31 UTC 2
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 2.0.3
numpy            : 1.24.3
pytz             : 2023.3
dateutil         : 2.8.2
setuptools       : 68.0.0
pip              : 23.2
Cython           : 0.29.36
pytest           : 7.4.0
hypothesis       : None
sphinx           : 7.0.1
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : 4.9.3
html5lib         : None
pymysql          : 1.4.6
psycopg2         : None
jinja2           : 3.1.2
IPython          : 8.14.0
pandas_datareader: None
bs4              : 4.12.2
bottleneck       : None
brotli           : None
fastparquet      : 2023.7.0
fsspec           : 2023.6.0
gcsfs            : None
matplotlib       : 3.7.2
numba            : 0.57.1
numexpr          : 2.8.4
odfpy            : None
openpyxl         : 3.1.2
pandas_gbq       : None
pyarrow          : 12.0.1
pyreadstat       : None
pyxlsb           : None
s3fs             : None
scipy            : 1.11.1
snappy           : None
sqlalchemy       : 1.4.49
tables           : 3.8.0
tabulate         : 0.9.0
xarray           : 2023.7.0
xlrd             : None
zstandard        : None
tzdata           : 2023.3
qtpy             : None
pyqt5            : None
@randolf-scholz randolf-scholz added Bug Needs Triage Issue that has not been reviewed by a pandas team member labels Jul 19, 2023
@lithomas1 lithomas1 added Testing pandas testing functions or related to the test suite IO Parquet parquet, feather Arrow pyarrow functionality Strings String extension data type and string data and removed Needs Triage Issue that has not been reviewed by a pandas team member Testing pandas testing functions or related to the test suite labels Aug 12, 2023
@randolf-scholz randolf-scholz mentioned this issue Aug 12, 2023
Open
3 tasks
@jorisvandenbossche jorisvandenbossche mentioned this issue Jul 29, 2024
Open
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@jorisvandenbossche jorisvandenbossche added this to the 2.3 milestone Nov 7, 2024
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Arrow pyarrow functionality Bug IO Parquet parquet, feather Strings String extension data type and string data
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Milestone
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