Вы можете использовать модуль CSV :
import csv
with open(your_file) as csv_in:
for row in csv.reader(csv_in):
row[2]+=row[3]
del row[3]
print(row)
Печать:
['test1', '2020-04-28', '00:00']
['test2', '2020-04-28', '00:15']
['test3', '2020-04-28', '00:30']
['test4', '2020-04-28', '00:45']
Вместо печати вы можете записать CSV в новый файл по адресу одновременно:
with open(your_file) as csv_in, open(your_new_file, 'w') as csv_out:
writer=csv.writer(csv_out)
for row in csv.reader(csv_in):
row[2]+=row[3]
del row[3]
writer.writerow(row)
your_new_file
становится:
test1,2020-04-28,00:00
test2,2020-04-28,00:15
test3,2020-04-28,00:30
test4,2020-04-28,00:45