BUG: drop_duplicates raises FutureWarning after resetting index

[tobiscode]

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(data={0: [0, 0, 3], 1: [1, 1, 0], "time": [0, 1, 2]})
df.set_index("time", inplace=True)
df.drop_duplicates(keep="last")

Issue Description

I get the following warning:

/home/tkoehne/apps/miniconda3/envs/testpd/lib/python3.10/site-packages/pandas/core/frame.py:6257: FutureWarning: In a future version, the Index constructor will not infer numeric dtypes when passed object-dtype sequences (matching Series behavior)
  diff = Index(subset).difference(self.columns)

Expected Behavior

Internally, the changing of the index and subsequent checks for dropping shouldn't raise a FutureWarning, but rather adopt the future behavior by default.

Installed Versions

/home/tkoehne/apps/miniconda3/envs/testpd/lib/python3.10/site-packages/_distutils_hack/init.py:33: UserWarning: Setuptools is replacing distutils.
warnings.warn("Setuptools is replacing distutils.")

INSTALLED VERSIONS

commit : ca60aab
python : 3.10.6.final.0
python-bits : 64
OS : Linux
OS-release : 4.18.0-348.2.1.el8_5.x86_64
Version : #1 SMP Mon Nov 8 13:30:15 EST 2021
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.4.4
numpy : 1.23.3
pytz : 2022.1
dateutil : 2.8.2
setuptools : 65.5.0
pip : 22.2.2
Cython : None
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : None
IPython : None
pandas_datareader: None
bs4 : None
bottleneck : 1.3.5
brotli : None
fastparquet : None
fsspec : None
gcsfs : None
markupsafe : None
matplotlib : None
numba : None
numexpr : 2.8.3
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : None
snappy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
zstandard : None

[dannyi96]

Have confirmed that this issue exists in latest released version 1.5 but is fixed in main ( for next 2.0 release ) via changes made in PR #49458 (in file pandas/core/indexes/base.py ).

[ CC: @mroeschke ]
would this be a change which would need to be backported to 1.5 as well ? or its fine for fix to be in next 2.0 release ?

[mroeschke]

Looks like #49458 fixed this because FutureWarning was removed to enforce the deprecation; therefore, it can't be backported to 1.5.2 since it would be a breaking change.

Overall this will be fixed in 2.0. A backport PR would be accepted, but it needs to be based on the 1.5.x branch.

[phofl]

I can see this on 1.4.4 but neither on 1.5.0 nor on 1.5.1,

[dannyi96]

@phofl yes, you're right ( my bad, the issue is present on older versions 1.4.x & is handled in 1.5.x )
I believe we can close this issue.