DOC: "Copy On Write: Patterns to avoid" confusion

[avm19]

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

https://pandas.pydata.org/docs/dev/user_guide/copy_on_write.html#patterns-to-avoid

Documentation problem

This code snippet

In [59]: df = pd.DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
In [60]: df2 = df.reset_index()
In [61]: df2.iloc[0, 0] = 100

is intended to illustrate that a copy (on write) will be created, because df and df2 reference the same data. In reality, no copy will be created because df2.iloc[0, 0] refers to the newly created integer column storing the reset index, which exists for df2, but not for df.

Suggested fix for documentation

Replace the last line of the snippet,

In [61]: df2.iloc[0, 0] = 100

with:

In [61]: df2.iloc[0, 1] = 100

[rhshadrach]

cc @phofl

[phofl]

Thx, very good catch