DOC: Code example doesn't run as shown

[saiwing-yeung]

Pandas version checks

• I have checked that the issue still exists on the latest versions of the docs on main here

Location of the documentation

pandas/doc/source/user_guide/copy_on_write.rst

Line 30 in 1a3230d

In [1]: df = pd.DataFrame({"foo": [1, 2, 3], "bar": [4, 5, 6]})

Documentation problem

In

pandas/doc/source/user_guide/copy_on_write.rst

Line 30 in 1a3230d

In [1]: df = pd.DataFrame({"foo": [1, 2, 3], "bar": [4, 5, 6]})

the doc has:

In [1]: df = pd.DataFrame({"foo": [1, 2, 3], "bar": [4, 5, 6]})
In [2]: df["foo"][df["bar"] > 5] = 100
In [3]: df
Out[3]:
   foo  bar
0  100    4
1    2    5
2    3    6

But running it should give

   foo  bar
0    1    4
1    2    5
2  100    6

Suggested fix for documentation

Change as above.

[ShaunSrirangam]

Hi I would like to take this issue

[ShaunSrirangam]

take

[jorisvandenbossche]

That code snippet is under the title "Previous behaviour", so it is expected that running that with the latest pandas gives a different result (that is the purpose of the section, to explain old behaviour).

We can probably make that more explicit with some extra code comment inside the code snippet, like # old behaviour with pandas < 3

[jorisvandenbossche]

Ah, sorry, I took a better look at your expected result now, and you meant that the updated value of 100 should be at the third instead of first row. That is entirely correct!