how to only keep columns with a certain regular expression code example

Example 1: pandas show column with regular expression

S=pd.Series(['Finland','Colombia','Florida','Japan','Puerto Rico','Russia','france'])
S.str.contains('^F.*')

Example 2: pandas show column with regular expression

import numpy as np
df['first_five_Letter']=df['Country (region)'].str.extract(r'(^\w{5})')
df.head()