Python Dataframe keep two different df

I run this code:

df=df_LtC
df["rolling"] = df["ln_ret"].rolling(window=2).mean() * 2

After running the function, I want to have df and df_LtC as different dataframes. I have no clue why to df_LtC is added the column ‘rolling’ becoming exactly the same as df.

df_LtC looks like this:

      date        variable       price    ln_ret
0   2000-01-01       low          2.03     NaN 
1   2000-01-01      close         2.39     0.16
2   2000-01-02       low          2.33    -0.02
3   2000-01-02      close         2.36     0.01

>Solution :

We should assign a copy of df_LtC to df to avoid such a behavior :

df = df_LtC.copy()