df_new[df_new['l_ext'].isin([31, 22, 30, 25, 64])]
type(x) is pd.DataFrame # NO
type(x) == pd.DataFrame # NO
isinstance(x, pd.DataFrame) # YES
In [21]: s.unique()
Out[21]: array(['a', 'b', 'c'], dtype=object)
In [22]: 'a' in s.unique()
Out[22]: True