Closed
Description
Pandas version checks
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I have checked that this issue has not already been reported.
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I have confirmed this issue exists on the latest version of pandas.
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I have confirmed this issue exists on the main branch of pandas.
Reproducible Example
This is as of pandas 1.4.3
>>> import pandas as pd
>>> pd.concat([pd.DataFrame({'a': range(10)}), pd.DataFrame({'b': range(10)})], sort=True, axis=1).index Int64Index([0, 1, 2, 3, 4, 5, 6, 7, 8, 9], dtype='int64')
Even though both inputs have identical RangeIndex inputs, the output index is an Int64Index. This behavior appears to be triggered by the sort=True parameter, since removing that gives a RangeIndex.
>>> pd.concat([pd.DataFrame({'a': range(10)}), pd.DataFrame({'b': range(10)})], axis=1).index
RangeIndex(start=0, stop=10, step=1)
My naive guess is that there is a missing check somewhere that the sort is a no-op on a RangeIndex .
This issue definitely seems related to #46675, but it is not identical since it has specifically appeared in 1.4.3, whereas that issue was already present in 1.4.2.
Installed Versions
```
commit : e8093ba
python : 3.8.13.final.0
python-bits : 64
OS : Linux
OS-release : 4.15.0-76-generic
Version : #86-Ubuntu SMP Fri Jan 17 17:24:28 UTC 2020
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : None
LOCALE : en_US.UTF-8
pandas : 1.4.3
numpy : 1.22.4
pytz : 2022.1
dateutil : 2.8.2
setuptools : 62.6.0
pip : 22.1.2
Cython : 0.29.30
pytest : 7.1.2
hypothesis : 6.47.1
sphinx : 5.0.2
blosc : None
feather : None
xlsxwriter : None
lxml.etree : 4.9.0
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.0.3
IPython : 8.4.0
pandas_datareader: None
bs4 : 4.11.1
bottleneck : None
brotli :
fastparquet : None
fsspec : 2022.5.0
gcsfs : None
markupsafe : 2.1.1
matplotlib : 3.5.2
numba : 0.55.2
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 8.0.0
pyreadstat : None
pyxlsb : None
s3fs : 2022.5.0
scipy : 1.8.1
snappy :
sqlalchemy : 1.4.38
tables : None
tabulate : 0.8.10
xarray : None
xlrd : None
xlwt : None
zstandard : None
```
Prior Performance
This is as of pandas 1.4.2
>>> pd.concat([pd.DataFrame({'a': range(10)}), pd.DataFrame({'b': range(10)})], sort=True, axis=1).index
RangeIndex(start=0, stop=10, step=1)