csv模块中DictReader将根据csv文件中每一行创建字典它会将标题视为键，将其下一行视为值
赋值后，迭代inputfile，打印每对字典，并在转换为整数后对每个值执行计算

from csv import DictReader

inputfile = DictReader(open('test.csv'))
for row in inputfile:
    print(f"{row['client']} profit : {int(row['revenue']) - int(row['expenses'])}")

# client_a profit : 550
# client_b profit : 800
# client_c profit : 1150

至少，你应该使用csv库。

import csv

with open("input.csv", "r") as file:
    mycsvfile = csv.reader(file, delimiter=",")
    
    for line, content in enumerate(mycsvfile):
        
        if line == 0:
            continue
        
        print("the client number {} is : {}".format(line, content[0]))
        
        print("the client number {} earns : {} $".format(line, content[1]))
        
        print("the client number {} spends {} $".format(line, content[2]))

输出将为

the client number 1 is : client_a
the client number 1 earns : 1000 $
the client number 1 spends 450 $
the client number 2 is : client_b
the client number 2 earns : 2000 $
the client number 2 spends 1200 $
the client number 3 is : client_c
the client number 3 earns : 1500 $
the client number 3 spends 350 $