REGR: inplace arithmetic operation on Series no longer updating parent DataFrame

[hjweide]

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• (optional) I have confirmed this bug exists on the master branch of pandas.

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Note: Please read this guide detailing how to provide the necessary information for us to reproduce your bug.

Code Sample, a copy-pastable example

import pandas as pd

df = pd.DataFrame({"A": [1, 2, 3]})

a = df["A"]
a += 999

print(df)
print(df["A"])

assert a is df["A"]

Problem description

I expect print(df) and print(df["A"]) to show identical values for column A. This is not the case. The output of the code above:

   A
0  1
1  2
2  3
0    1000
1    1001
2    1002
Name: A, dtype: int64

Expected Output

   A
0  1000
1  1001
2  1002
0    1000
1    1001
2    1002
Name: A, dtype: int64

Output of pd.show_versions()

INSTALLED VERSIONS

commit : fd20f7d
python : 3.8.2.final.0
python-bits : 64
OS : Linux
OS-release : 5.4.0-47-generic
Version : #51-Ubuntu SMP Fri Sep 4 19:50:52 UTC 2020
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.2.0.dev0+379.gfd20f7d34
numpy : 1.19.2
pytz : 2020.1
dateutil : 2.8.1
pip : 20.0.2
setuptools : 44.0.0
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 : None
fsspec : None
fastparquet : None
gcsfs : None
matplotlib : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pytables : None
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
numba : None
None

Possibly related to #36051?

[dsaxton]

This is a regression from 1.0.5 and seems this line is the cause:

pandas/pandas/core/ops/methods.py

Line 97 in fd20f7d

self._reset_cacher()

---

a3097b5 is the first bad commit
commit a3097b5
Author: rjfs rafajfsantos@gmail.com
Date: Thu Mar 26 13:53:13 2020 +0100

BUG: Fixed strange behaviour of pd.DataFrame.drop() with inplace argu… (#30501)

doc/source/whatsnew/v1.1.0.rst | 1 +
pandas/core/ops/methods.py | 3 ++-
pandas/tests/frame/test_axis_select_reindex.py | 21 +++++++++++++++++++++
3 files changed, 24 insertions(+), 1 deletion(-)

[simonjayhawkins]

This is a regression from 1.0.5 and seems this line is the cause:

@dsaxton I think helps to add the PR number so that github creates a link (I have found duplicate issues in the past by doing this)

#30501

[simonjayhawkins]

moved off 1.1.3 milestone, see #36498 (comment)

[simonjayhawkins]

moved off 1.1.4 milestone (scheduled for release tomorrow)

[jorisvandenbossche]

Since the consensus on the PR seems to be to revert the original patch, let me quickly do that.

[simonjayhawkins]

Since the consensus on the PR seems to be to revert the original patch, let me quickly do that.

if you need to feel free to put a note in other, i'll update #37496 if necessary.