If else Function with several conditions -Python

I am trying to calculate the final revenue of my dataset. My dataset has several revenue streams, but given some conditions (that I will explain later) the revenue per client will be calculated differently for the final revenue.

I am not very comfortable creating functions yet so I'm not sure where I am making mistakes.

Dataframe examples:

ClientId   Sector    Class    Rev1    Rev2    Rev3
1          Sect_1    B        5       1       0 
2          Sect_2    A        5.5     2       0
3          Sect_3    B        6       1.5     1
4          Sect_4    A        5       1       1.5
5          Sect_5    B        5       2       1

I want to create a 7th column 'Final_Rev' given the following conditions:

- If 'Sector' = (Sect_3 or Sect_4) : 'Final_Rev' = Rev2 + Rev3
- OR if 'Class' = ("A") : 'Final_Rev' = Rev2 + Rev3
- Otherwise 'Final_Rev' = Rev1

Expected Output should be the following:

ClientId   Sector    Class    Rev1    Rev2    Rev3    Final_Rev
1          Sect_1    B        5       1       0       5
2          Sect_2    A        5.5     2       0       2
3          Sect_3    B        6       1.5     1       2.5
4          Sect_4    A        5       1       1.5     2.5
5          Sect_5    B        5       2       1       5

I have tried to create the following function but I'm not sure what I'm doing wrong:

def Final_Rev():
    
    if Sector in ['Sect_3','Sect_4'] or Class == 'A':
        return df['Rev2'] + df['Rev3']
    else: 
        return df['Rev1']

df['Final_Rev'] = df.apply(Final_Rev, axis=1)

I have found an R solution that does what I want but I don't know how to convert it to python:

Final_Rev := ifelse(test = (Sector %in% c("Sect_3","Sect_4")|Class == "A"),
             yes = Rev2 + Rev3,
             no = Rev1

If someone could help me solve this, it would be really appreciate. Thanks.