Overwriting a specific row in a csv file using Python's CSV module

Question

I'm using Python's csv module to do some reading and writing of csv files.

I've got the reading fine and appending to the csv fine, but I want to be able to overwrite a specific row in the csv.

For reference, here's my reading and then writing code to append:

    #reading
    b = open("bottles.csv", "rb")
    bottles = csv.reader(b)
    bottle_list = []
    bottle_list.extend(bottles)
    b.close()

    #appending
    b=open('bottles.csv','a')
    writer = csv.writer(b)
    writer.writerow([bottle,emptyButtonCount,100, img])
    b.close()

And I'm using basically the same for the overwrite mode(which isn't correct, it just overwrites the whole csv file):

    b=open('bottles.csv','wb')
    writer = csv.writer(b)
    writer.writerow([bottle,btlnum,100,img])
    b.close()

In the second case, how do I tell Python I need a specific row overwritten? I've scoured Gogle and other stackoverflow posts to no avail. I assume my limited programming knowledge is to blame rather than Google.

Answer 1

I will add to Steven Answer :

import csv

bottle_list = []

# Read all data from the csv file.
with open('a.csv', 'rb') as b:
    bottles = csv.reader(b)
    bottle_list.extend(bottles)

# data to override in the format {line_num_to_override:data_to_write}. 
line_to_override = {1:['e', 'c', 'd'] }

# Write data to the csv file and replace the lines in the line_to_override dict.
with open('a.csv', 'wb') as b:
    writer = csv.writer(b)
    for line, row in enumerate(bottle_list):
         data = line_to_override.get(line, row)
         writer.writerow(data)

Answer 2

You cannot overwrite a single row in the CSV file. You'll have to write all the rows you want to a new file and then rename it back to the original file name.

Your pattern of usage may fit a database better than a CSV file. Look into the sqlite3 module for a lightweight database.