to_numpy() works in jupyter notebook, but not in python script

[bluefrog]

Hi

I am unsure why the following works in a jupyter notebook, but not in a python script that I am run from the Linux command line:

#!/usr/bin/python3
import pandas as pd
import numpy as np

# SWAPPING COLUMNS

dates=pd.date_range('1/1/2019',periods=12)
df=pd.DataFrame(np.random.randn(12,4),index=dates,columns=['A','B','C','D'])

df_copy=df.copy()
# assign, after converting to raw data
df_copy.loc[: ['B', 'A']]=df_copy[['A','B']].to_numpy()
print(df_copy)

Any suggestions ?