How to fix the code about appending a number in the line? - python-3.x

Question

I create a new column (name:Account) in the csv, then try to make a sequence (c = float(a) + float(b)) and for each number in sequence append to the original line in the csv, which is the value of the new column. Here is my code:
# -*- coding: utf-8 -*-
import csv
with open('./tradedate/2007date.csv') as inf:
reader = csv.reader(inf)
all = []
row = next(reader)
row.append('Amount')
all.append(row)
a =50
for i, line in enumerate(inf):
if i != 0:
size = sum(1 for _ in inf) # count the line number
for b in range(1, size+1):
c = float(a) + float(b) # create the sequence: in 1st line add 1, 2nd line add 2, 3rd line add 3...etc
line.append(c) # this is the error message: AttributeError: 'str' object has no attribute 'append'
all.append(line)
with open('main_test.csv', 'w', newline = '') as new_csv:
csv_writer = csv.writer(new_csv)
csv_writer.writerows(all)
The csv is like this:
日期,成交股數,成交金額,成交筆數,發行量加權股價指數,漲跌點數,Account
96/01/02,"5,738,692,838","141,743,085,172","1,093,711","7,920.80",97.08,51
96/01/03,"5,974,259,385","160,945,755,016","1,160,347","7,917.30",-3.50,52
96/01/04,"5,747,756,529","158,857,947,106","1,131,747","7,934.51",17.21,53
96/01/05,"5,202,769,867","143,781,214,318","1,046,480","7,835.57",-98.94,54
96/01/08,"4,314,344,739","115,425,522,734","888,324","7,736.71",-98.86,55
96/01/09,"4,533,381,664","120,582,511,893","905,970","7,790.01",53.30,56
The Error message is:
Traceback (most recent call last):
File "main.py", line 21, in <module>
line.append(c)
AttributeError: 'str' object has no attribute 'append'
Very thanks for any help!!

Answer 1

I'm a little confused why you're structuring your code this way, but the simplest fix would be to change the append (since you can't append to a string) to += a string version of c, i.e.
line += str(c)
or
line += ',{}'.format(c)
(I'm not clear based on how you're written this if you need the comma or not)
The biggest problem is that you're not using your csv reader - below is a better implementation. With the csv reader it's cleaner to do the append that you want to do versus using the file object directly.
import csv
with open('./tradedate/2007date.csv') as old_csv:
with open('main_test.csv', 'w') as new_csv:
writer = csv.writer(new_csv, lineterminator='\n')
reader = csv.reader(old_csv)
all = []
row = next(reader)
row.append('Line Number')
all.append(row)
line_number = 51
for row in reader:
row.append(line_number)
all.append(row)
line_number += 1
writer.writerows(all)