Why the inserted new column to a copied dataframe will be added to the original dataframe too? [duplicate]

Answer 1

Use assign which creates a copy of the old dataframe:

df_old = pd.DataFrame({'a': [1, 2], 'b': [3, 4]})
df_new = df_old.assign(c=[5,6])
print(df_old)
print(df_new)

Output:

   a  b
0  1  3
1  2  4
   a  b  c
0  1  3  5
1  2  4  6