pandas: BUG: Augmented arithmetic assignments will modify original series starting version 1.1.4

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I have confirmed this bug exists on the latest version of pandas.
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Code Sample, a copy-pastable example

import pandas as pd

s = pd.Series([1, 2, 3])
s1 = s.iloc[1:]
s1 -= 4
s

# output
# 0    1
# 1   -2
# 2   -1
# dtype: int64

s = pd.Series([1, 2, 3])
s1 = s.iloc[1:]
s1 = s1 - 4
s

# output
# 0    1
# 1    2
# 2    3
# dtype: int64

Problem description

Starting with version 1.1.4 when applying either of +=, -=, *= or /= operators on a series s1 that was sliced from original series s, the change propagates to original series s. When using normal assignment operators s1 = s1 - 4 the problem is not present, which leads to inconsistent behavior.

Output of `pd.show_versions()`

INSTALLED VERSIONS

commit : 67a3d4241ab84419856b84fc3ebc9abcbe66c6b3 python : 3.7.9.final.0 python-bits : 64 OS : Windows OS-release : 10 Version : 10.0.18362 machine : AMD64 processor : Intel64 Family 6 Model 158 Stepping 13, GenuineIntel byteorder : little LC_ALL : None LANG : None LOCALE : None.None

pandas : 1.1.4 numpy : 1.17.2 pytz : 2020.4 dateutil : 2.8.0 pip : 20.3.3 setuptools : 51.0.0.post20201207 Cython : 0.28.5 pytest : 3.8.1 hypothesis : None sphinx : None blosc : None feather : None xlsxwriter : None lxml.etree : None html5lib : None pymysql : None psycopg2 : None jinja2 : 2.11.2 IPython : 7.19.0 pandas_datareader: None bs4 : None bottleneck : None fsspec : None fastparquet : None gcsfs : None matplotlib : 3.3.3 numexpr : None odfpy : None openpyxl : None pandas_gbq : None pyarrow : None pytables : None pyxlsb : None s3fs : None scipy : 1.5.4 sqlalchemy : None tables : None tabulate : None xarray : None xlrd : None xlwt : None numba : None

About this issue

Original URL
State: closed
Created 4 years ago
Comments: 18 (11 by maintainers)

Commits related to this issue

add code sample for #38519 — committed to simonjayhawkins/pandas by simonjayhawkins 4 years ago

Most upvoted comments

Sure. Sorry for taking a while. I’ve unassigned myself. Thanks.

SophiaTangHart on Jan 25, 2023

I’d like to take it and clarify on the release note. I’d like to let you know that this is my first time contributing.

SophiaTangHart on Oct 18, 2022