PYTHON

A value is trying to be set on a copy of a slice from a DataFrame.

# Error:
# SettingWithCopyWarning: A value is trying to be set on a copy of a
# slice from a DataFrame

# As explained in the Source, this warning is usually safe to ignore. You
# can disable it by running the following:

import pandas as pd
pd.options.mode.chained_assignment = None  # default='warn'

A value is trying to be set on a copy of a slice from a DataFrame. Try using .loc[row_indexer,col_indexer] = value instead

df[df['A'] > 2]['B'] = new_val  # new_val not set in df
# rewrite it as below
df.loc[df['A'] > 2, 'B'] = new_val