Inline CSV File Editing with Python

There is no underlying system call for inserting data into a file. You can overwrite, you can append, and you can replace. But inserting data into the middle means reading and rewriting the entire file from the point you made your edit down to the end.

As such, the two ways to do this are either (a) slurp the entire file into memory, make your edits there, and then dump the result back to disk, or (b) open up a temporary output file where you write your results while you read the input file, and then replace the old file with the new one once you get to the end. One method uses more ram, the other uses more disk space.

No, you should not attempt to write to the file you are currently reading from. You can do it if you keep seeking back after reading a row but it is not advisable, especially if you are writing back more data than you read.

The canonical method is to write to a new, temporary file and move that into place over the old file you read from.

from tempfile import NamedTemporaryFile
import shutil
import csv

filename = 'tmpEmployeeDatabase.csv'
tempfile = NamedTemporaryFile('w+t', newline='', delete=False)

with open(filename, 'r', newline='') as csvFile, tempfile:
    reader = csv.reader(csvFile, delimiter=',', quotechar='"')
    writer = csv.writer(tempfile, delimiter=',', quotechar='"')

    for row in reader:
        row[1] = row[1].title()
        writer.writerow(row)

shutil.move(tempfile.name, filename)

I've made use of the tempfile and shutil libraries here to make the task easier.