cur.execute('SELECT dogovor, number, rub, kop FROM dolg')
            rows = cur.fetchall()
            for row in rows:
                fp = open('dolg.csv', 'w')
                my_file = csv.writer(fp, delimiter='\t', lineterminator='\n')
                my_file.writerows(rows)

                 lst0 = ('-'.join(row[0][i:i + 2] for i in range(0, len(row[0]), 2)))
                print(lst0, row[1], row[2], row[3])

  
>>> import re
>>> 
>>> row = ['1234567890', '1', '123', '456']
>>> 
>>> row_new = ['-'.join(re.findall(r'..', row[0]))] + row[1:]
>>> 
>>> row
['1234567890', '1', '123', '456']
>>> row_new
['12-34-56-78-90', '1', '123', '456']
>>>

 import csv
def ReadCSV():
    with open('dolg.csv') as File:
        reader = csv.reader(File, delimiter='\t')
        for row in reader:
            # Через срез
            data = [('-'.join(row[0][i:i + 2] for i in range(0, len(row[0]), 2))), row[1], row[2], row[3]]
            # Выводит как надо
            print(data)
            my_file = open('example2.csv', 'w')
            with my_file:
                writer = csv.writer(my_file, delimiter='\t')
                writer.writerows(data)
    print("Writing complete")
if __name__ == '__main__':
    ReadCSV()

  
>>> import io
>>> 
>>> stream = io.StringIO()
>>> 
>>> import csv
>>> 
>>> data = ['12-34-56-78-90', 'a', 'b', 'c']
>>> 
>>> writer = csv.writer(stream, delimiter='\t')
>>> writer.writerows(data)
>>> 
>>> stream.seek(0)
0
>>> stream.read()
'1\t2\t-\t3\t4\t-\t5\t6\t-\t7\t8\t-\t9\t0\r\na\r\nb\r\nc\r\n'
>>>

  
>>> import io
>>> 
>>> stream = io.StringIO()
>>> 
>>> import csv
>>> 
>>> data = ['12-34-56-78-90', 'a', 'b', 'c']
>>> 
>>> writer = csv.writer(stream, delimiter='\t')
>>> writer.writerow(data)
22
>>> 
>>> stream.seek(0)
0
>>> stream.read()
'12-34-56-78-90\ta\tb\tc\r\n'
>>>

 rows = cur.fetchall()