How to check if a value is in the list in selection from pandas data frame?

You can use pd.DataFrame.query:

select_values = [31, 22, 30, 25, 64]
df_cut = df_new.query('l_ext in @select_values')

In the background, this uses the top-level pd.eval function.

Use isin

df_new[df_new['l_ext'].isin([31, 22, 30, 25, 64])]