df[df['A'] > 2]['B'] = new_val # new_val not set in df
The warning offers a suggestion to rewrite as follows:
df.loc[df['A'] > 2, 'B'] = new_val
However, this doesn’t fit your usage, which is equivalent to:
df = df[df['A'] > 2] df['B'] = new_val
While it’s clear that you don’t care about writes making it back to the original frame (since you are overwriting the reference to it), unfortunately this pattern cannot be differentiated from the first chained assignment example. Hence the (false positive) warning. The potential for false positives is addressed in the docs on indexing, if you’d like to read further. You can safely disable this new warning with the following assignment.
import pandas as pd pd.options.mode.chained_assignment = None # default='warn'