Python. Code leaves blank rows in csv file after every row

Question

Why code deletes not only winningRows, but also csv header row and leaves blank row after every row? How to fix it? I only need to delete winningRows, no blank rows needed.

def generate():
    global winningRows
    filename = enterFile()

    noOfWinners = 5
    winningNumbers = []
    while len(winningNumbers) < noOfWinners:
        luckyNumber = random.randint(1, totalEntries)
        if luckyNumber not in winningNumbers:
            winningNumbers.append(luckyNumber)

    with open(filename, newline="") as entriesCSV:
        entriesDict = csv.DictReader(entriesCSV,dialect="excel")
        allRows = [row for row in entriesDict]
        winningRows = [row for row in allRows if int(row["#"]) in winningNumbers]
        nonWinningRows = [row for row in allRows if int(row["#"]) not in winningNumbers]
        for row in winningRows:
            winnerName = row["Name"]
            winnerID = row["ID"]
            winnerEmail = row["Email"]
            print(f"The winner is {winnerName}, ID {winnerID}, email {winnerEmail}")

        csv.DictWriter(open(filename, "w"), fieldnames=["#", "Name", "ID", "Email"]).writeheader()
        csv.DictWriter(open(filename, "w"), fieldnames=["#", "Name", "ID", "Email"]).writerows(nonWinningRows)

csv before running the code

csv after running the code

It seems this is working:

with open(filename, newline='\n') as entriesCSV:
    entriesDict = csv.DictReader(entriesCSV,dialect="excel")
    allRows = [row for row in entriesDict]
    winningRows = [row for row in allRows if int(row["#"]) in winningNumbers]
    nonWinningRows = [row for row in allRows if int(row["#"]) not in winningNumbers]
    for row in winningRows:
        winnerName = row["Name"]
        winnerID = row["ID"]
        winnerEmail = row["Email"]
        print(f"The winner is {winnerName}, ID {winnerID}, email {winnerEmail}")

with open(filename, "w", newline='\n') as entriesCSV:
    writer = csv.DictWriter(entriesCSV, fieldnames=["#", "Name", "ID", "Email"])
    writer.writeheader()
    writer.writerows(nonWinningRows)

But in this case, I am opening the file twice, right?

Answer 1

Looks like you are on Windows. Add the newline argument to your open function.

with open(filename, "w", newline='\n') as fp:
    writer = csv.DictWriter(fp, fieldnames=["#", "Name", "ID", "Email"])
    writer.writeheader()
    writer.writerows(nonWinningRows)

Answer 2

You are opening the same file multiple times in parallel. I can't test this without the data, but does this work?

with open(filename, newline="") as entriesCSV:
    entriesDict = csv.DictReader(entriesCSV,dialect="excel")

allRows = [row for row in entriesDict]
winningRows = [row for row in allRows if int(row["#"]) in winningNumbers]
nonWinningRows = [row for row in allRows if int(row["#"]) not in winningNumbers]
for row in winningRows:
    winnerName = row["Name"]
    winnerID = row["ID"]
    winnerEmail = row["Email"]
    print(f"The winner is {winnerName}, ID {winnerID}, email {winnerEmail}")

with open(filename, "w") as outputCSV:
    writer = csv.DictWriter(outputCSV, fieldnames=["#", "Name", "ID", "Email"])
    writer.writeheader()
    writer.writerows(nonWinningRows)