How to change the separator used in a CSV file?

For a study project I have many many csv files that I need to change from comma (,) separated to semicolon (;) separated. So I only need to change the separator.

I normally do it in Excel, but that takes a lot of work. And there I need to do it for every file separately plus Excel take a lot of time to do it.

I have made a input and output folder. That works fine in the code below. The problem is:

1. the comma is not getting changed in a semicolon.
2. and for some reason it is adding a blank line, I don’t know why it does that.

Can somebody give some tips?

import csv 
from pathlib import Path

folder_in = Path(r'C:\convert\Trajectory\In') 
folder_out = Path(r'C:\convert\Trajectory\Out')

for incsv in folder_in.iterdir():
    outcsv = folder_out.joinpath(incsv.name)
    with open(str(incsv), 'r') as fin, open(str(outcsv), 'w') as fout:
        reader = csv.DictReader(fin)
        writer = csv.DictWriter(fout, reader.fieldnames, delimiter=';')
        writer.writeheader()
        writer.writerows(reader)