Adding/appending additional information in a column for a csv file

Question

EDIT:

I need to store/add/append additional information in a specific column in a csv file with out using csv.DictReader.

If I wanted to skip a row in a column and it was empty, what do I need to do for it?

For example:

Sample csv file:

$ cat file.csv
"A","B","C","D","E"
"a1","b1","c1","d1","e1"
"a2","b2","c2","d2","e2"
"a2","b2","c2",,"e2"

Code:

sample = ['dx;dy']
with(openfile.csv, "r") as csvfile:
    reader = csv.reader(csvfile, delimiter=',', quotechar='"')
    headers = next(reader)
    for row in reader:
        #sample.append(to the column D)

The Output should look like this:

$ cat file.csv
    "A","B","C","D","E"
    "a1","b1","c1","d1;dx;dy","e1"
    "a2","b2","c2","d2;dx;dy","e2"
    "a2","b2","c2",,"e2"

`sample = ['dx';'dy']` is invalid syntax. Please fix this. Did you mean `sample = 'dx;dy'`? — Pranav Hosangadi, Apr 01 '22 at 19:21
Can you also specify how you know you want to append to column `"D"` and what character to separate the existing value and the new value by? My answer assumes both these are given. — Pranav Hosangadi, Apr 01 '22 at 19:33
Thank you Pranav! <3 If i wanted to skip a row for appending the column what would I need to do? PLease see my edit — CanadianGirl827x, Apr 01 '22 at 20:24
See what you get in `row` for that third row (either by printing the rows as you read them, or by stepping through your code in a debugger). How would you check if the `value` is equal to that? — Pranav Hosangadi, Apr 01 '22 at 20:29
Right! And you only want to make the modification if that is _not_ the case, so do `if value != "": new_value = ..., row[col_index] = ...` — Pranav Hosangadi, Apr 01 '22 at 21:09
Btw, empty strings are [falsy](https://stackoverflow.com/q/39983695/843953), so you could just do `if value` instead of `if value != ""` — Pranav Hosangadi, Apr 01 '22 at 21:10

Pranav Hosangadi · Accepted Answer · 2022-04-01T19:31:52.373

Since you know the header of the column you want to append to, you can find its index in the headers row, and then modify that element of each row.

append_to_column = 'D'
separator = ';'
sample = ['dx;dy']
with open('file.csv', "r") as csvfile, open("outfile.csv", "w") as outfile:
    reader = csv.reader(csvfile, delimiter=',', quotechar='"')
    headers = next(reader)
    writer = csv.writer(outfile, delimiter=',', quotechar='"')
    col_index = headers.index(append_to_column)
    for row in reader:
        value = row[col_index]
        new_value = value + separator + sample[0]
        row[col_index] = new_value
        writer.writerow(row)

Which gives:

A,B,C,D,E
a1,b1,c1,d1;dx;dy,e1
a2,b2,c2,d2;dx;dy,e2

Note that this file doesn't have quotes because they aren't required, since the fields don't contain any commas. If you want to force the csv.writer to write quotes, you can add the quoting=csv.QUOTE_ALL argument to the csv.writer() call, like so: writer = csv.writer(outfile, delimiter=',', quotechar='"', quoting=csv.QUOTE_ALL) Then, you'll get:

"A","B","C","D","E"
"a1","b1","c1","d1;dx;dy","e1"
"a2","b2","c2","d2;dx;dy","e2"

Adding/appending additional information in a column for a csv file

1 Answers1