python - How to find the line that is generating a Pandas SettingWithCopyWarning?

Question

I have a large block of code that is, at some point somewhere, generating a setting with copy warning in pandas (this problem).

I know how to fix the problem, but I can't find what line number it is! Is there a way to back out the line number (apart from brute force methods like debug-stepping or putting in multiple prints)? The only output I get is the below, which doesn't go up the stack to my code:

C:Anaconda3libsite-packagespandascoreframe.py:2302: SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame  **kwargs)

question from:https://stackoverflow.com/questions/30392099/how-to-find-the-line-that-is-generating-a-pandas-settingwithcopywarning

Answer 1

Set pd.options.mode.chained_assignment = 'raise'

This will throw an exception pointing to the line which triggers SettingWithCopyError.

UPDATE: how to catch the error, and interrogate the stacktrace to get the actual offending lineno:

import pandas as pd
from inspect import currentframe, getframeinfo
from pandas.core.common import SettingWithCopyError

pd.options.mode.chained_assignment = 'raise'

df = pd.DataFrame({'a': [1, 2, 3], 'b': [4, 5, 6]})

df2 = df[df['a'] == 2]

try:
    df2['b'] = 'foo'
except SettingWithCopyError:
    print('handling..')
    frameinfo = getframeinfo(currentframe())
    print(frameinfo.lineno)