REGR: invalid cache after take operation with non-consolidated dataframe

[on55]

a program run ok with pandas 1.0.5, but after upgrade to 1.1.0. it fail.
i found sometimes when I change one cell of dataframe value, print(df) and it doesn't change.
but i use ==, it says changed.
for example: original cell value is A, then i change cell value to B. A=B
print df, it show still A
df.at(x, x) == B, it says TRUE.

---

MarcoGorelli's edit: here's a reproducible example:

import pandas as pd


position = pd.DataFrame(columns=["code", "startdate"])
position = position.append([{"code": "a", "startdate": 0}])

# These two lines should not change anything.
# BUT, commenting either of them out makes this code run as intendeed
position["code"] == "A"
position[position["startdate"] == 0]

position.at[0, "code"] = "A"

print(position.at[0, "code"])
print(position)

output:

A
  code startdate
0    a         0

expected output:

A
  code startdate
0    A         0

[jreback]

pls show an example that reproduces the issue

[MarcoGorelli]

Closing as I can't reproduce this:

>>> import pandas as pd
>>> df = pd.DataFrame({'a': ['A']})
>>> df
   a
0  A
>>> df.loc[0, 'a'] = 'B'
>>> df.at[0, 'a'] == 'B'
True
>>> print(df)
   a
0  B

Please ping if you can provide a bug report as is suggested here https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports

[MarcoGorelli]

@simonjayhawkins noticed you'd put the 1.1.1 milestone - were you able to reproduce this?

[on55]

MarcoGorelli：
Nice to meet you! sorry i seldom come to here and just see your comments.

Details is:
The program read many data and calculate.
after program calculate and output a big dataframe, then program change several value of the left 1st column in a cycle.
the sentence is 'position.at[index, 'code'] = code‘.
only one cell's value can not be changed.
when i print(df) , it show original value. i use 'df.at[x, y] == new value' it say TRUE.
i use 'df.at[x, y] == original value' it say FALSE.
since this sentence is ran in a cycle, other cell's values are changed correctly, only one cell value meet this problem.

now i have degraded to 1.0.5 and my program run ok again.
my program run ok with many pandas version, just have issue with pandas 1.1.0.
so i suppose there may be memory corruption for that version.

thank you and thank pandas.

[on55]

supplement：
the dataframe is a little big and produced by program automatic, it is not a simple dataframe with 1X1 matrix.
program change left 1st column's several cell value in a loop , and only one cell meet this issue, other cell value is changed well.

the cell value printed show original value,
when i use == new value it say TRUE.
it looks like value is changed and just print issue.

following program continue run and report error.
because following program read dataframe and find the cell value still is original value, it doesn't changed.
following program can not get correct code value，so it report error.

[simonjayhawkins]

@simonjayhawkins noticed you'd put the 1.1.1 milestone - were you able to reproduce this?

not tried to reproduce. using the 1.1.1 milestone as a tracker (for regressions and related PRs). 1.1.1 will be released next week and any items on the milestone still open at that time will be moved to 1.1.2 (or can review). the blocker tag can be used, but less relevant for a patch release as 1.1.2 could follow in 2-3 weeks.

for the minor releases (i.e 1.2) it is common to only apply the milestone when the PR is close to be ready (and then also on the corresponding issue)

when triaging issues i tend to either tag as 1.1.1(for regressions from 1.0.5) or contributions welcome (bugs and regressions from earlier versions)