I have a CSV file as follows.

oldFile.csv content:

oldHeader1,oldHeader2,oldHeader3
data01,data02,data03
data11,data12,data13
data21,data22,data23

and I want to rename the headers with new ones. Here’s the code I use to do this:

import csv

with open("oldFile.csv", "r") as input:
    reader = csv.DictReader(input, delimiter=",")
    reader.fieldnames = ["newHeader1", "newHeader2", "newHeader3"]
    rows = list(reader)
    with open("newFile.csv", "w", newline="") as output:
        writer = csv.DictWriter(output, fieldnames=reader.fieldnames, delimiter=",")
        writer.writeheader()
        for row in rows:
            writer.writerow(row)

The problem is that it doesn’t change the headers, but adds new ones.

newFile.csv content:

newHeader1,newHeader2,newHeader3
oldHeader1,oldHeader2,oldHeader3
data01,data02,data03
data11,data12,data13
data21,data22,data23

I could delete the first line before defining the new headers, but referring to other stackoverflow questions (e.g. here or here) I have the impression that it should work without and that I’m doing something wrong.

What’s the proper way to achieve this?