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Reproducible Example

import warnings import pandas as pd df = pd.DataFrame({"A": [0, 1], "B": [2, 3], "C": [4, 5]}) for _ in range(3): # Normal behaviour (warning will display once). warnings.warn("First warning.") for _ in range(3): warnings.warn("Second warning.") # Select two columns from the DataFrame. # This line seems to affect the behaviour of the second # warning - it will display on all 3 iterations of the loop. df = df[["A", "B"]]

Issue Description

Selecting columns from a DataFrame appears to affect the normal behaviour of Python warnings.

Where a warning is raised repeatedly by a given line within a loop, the default behaviour is that the warning will only be displayed the first time it is raised. This is what happens in the first loop above.

However, in the second loop, the line which filters the columns of the DataFrame (df = df[["A", "B"]]) seems to affect this behaviour, as this time the warning is displayed on each iteration of the loop, rather than just once. Interestingly, this behaviour occurs regardless of whether this filtering line appears before or after the second warn() statement.

The following is the output produced:

..\repeated_warnings.py:8: UserWarning: First warning. warnings.warn("First warning.") ..\repeated_warnings.py:11: UserWarning: Second warning. warnings.warn("Second warning.") ..\repeated_warnings.py:11: UserWarning: Second warning. warnings.warn("Second warning.") ..\repeated_warnings.py:11: UserWarning: Second warning. warnings.warn("Second warning.")

I've experimented with putting warnings.resetwarnings() at the start of the script and then examining the contents of the warnings.filters list immediately prior to the two warn() statements - I thought perhaps Pandas might be adding filters to the filters list. However, in each case the filters list seems to be empty, so that doesn't seem to be the problem.

This may be in some way related to Issue #55801, although that issue relates to creation of a DataFrame, rather than selecting columns from it.

Expected Behavior

I would expect each warning to display only once:

..\repeated_warnings.py:8: UserWarning: First warning. warnings.warn("First warning.") ..\repeated_warnings.py:11: UserWarning: Second warning. warnings.warn("Second warning.")

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