Как задать условие для замены слов в тексте (DataFrame Python)

print(data['purpose'].value_counts())
 
wedding ceremony                            797
having a wedding                            777
to have a wedding                           774
housing                                     647
purchase of the house                       647
purchase of the house for my family         641
construction of own property                635
property                                    634
transactions with my real estate            630
building a real estate                      626
buy real estate                             623
buying my own car                           505
going to university                         496
car                                         495
second-hand car purchase                    489
to own a car                                480
buying a second-hand car                    479
cars                                        478
to buy a car                                472
education                                   447
getting an education                        443
profile education                           436
getting higher education                    426
to become educated                          412
Name: purpose, dtype: int64

for purpose in data['purpose']:
    if 'wedd' in purpose:
        purpose = 'wedding'
    else:
        if 'estate' in purpose:
            purpose = 'wedding'

import pandas as pd
df = pd.DataFrame(['$$a', '$$b', '$c'], columns=['f'])
 
df[df['f'].str.contains('a') == True]  = 'Замена'
 
print(df)