==== swap columns ====
<code>
$ ipython
Python 3.11.4 | packaged by Anaconda, Inc. | (main, Jul  5 2023, 13:47:18) [MSC v.1916 64 bit (AMD64)]
IPython 8.12.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]:
import pandas as pd
data = {'Spam': [0.0,  1.0],
        'Ham' : [1.0,  0.0],
        'PT1' : [0.11, 0.12],
        'PT2' : [0.21, 0.22],
        'PT3' : [0.31, 0.32],
        'PT4' : [0.41, 0.42]}
df = pd.DataFrame(data)
df
Out[1]:
   Spam  Ham   PT1   PT2   PT3   PT4
0   0.0  1.0  0.11  0.21  0.31  0.41
1   1.0  0.0  0.12  0.22  0.32  0.42

In [2]:
df[['PT2', 'PT1']] = df[['PT1', 'PT2']]
df
Out[2]:
   Spam  Ham   PT1   PT2   PT3   PT4
0   0.0  1.0  0.21  0.11  0.31  0.41
1   1.0  0.0  0.22  0.12  0.32  0.42

In [3]:
pd.__version__
Out[3]:
'1.5.3'
</code>

Ref:-
  * Got the sample data from https://stackoverflow.com/questions/57446160/swap-or-exchange-column-names-in-pandas-dataframe-with-multiple-columns and tweaked the data and column names a bit.
  * https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#basics
    * Says that the correct way to swap two columns is <code>
df.loc[:, ['B', 'A']] = df[['A', 'B']].to_numpy()
</code>