[Python] Extra newline before -----END CERTIFICATE----- when processing CSV in Python

I'm processing CSV files in Python to extract and format data from another file. However, when writing the output, I get an extra newline before -----END CERTIFICATE-----. I want the output to have print one newline before -----END CERTIFICATE-----, but my current code adds an extra blank line its like its escaping it and i don't understand why

i tried using.strip() on the certificate and public key to remove any leading or trailing whitespace, but the extra newline still appeared.

The begin certificate part is correct with -----BEGIN CERTIFICATE----- \n but the ending isnt

Any advice on how to correct this?

import csv
import os

# Define input files and output file
input_files = ['11296205_124_2025.csv', '11296208_113_2025.csv']
output_file = 'inventory_upload.csv'

# Prepare the output data list
converted_data = []

# Process each input file
for input_file in input_files:
if not os.path.exists(input_file):
print(f"Warning: {input_file} not found, skipping.")
continue

with open(input_file, mode='r', encoding='utf-8') as infile:
reader = csv.DictReader(infile)
for row in reader:
# Get the certificate and key values
tpm_certificate = row['TPM Certificate'].strip()
gek_public_key = row['GEK Public Key'].strip()

# Remove existing markers and normalize newlines
tpm_certificate = tpm_certificate.replace("-----BEGIN CERTIFICATE-----", "").replace("-----END CERTIFICATE-----", "")
gek_public_key = gek_public_key.replace("-----BEGIN PUBLIC KEY-----", "").replace("-----END PUBLIC KEY-----", "")

# Ensure there are no extra empty lines
tpm_certificate = "\n".join([line.strip() for line in tpm_certificate.splitlines() if line.strip()])
gek_public_key = "\n".join([line.strip() for line in gek_public_key.splitlines() if line.strip()])

# Correctly format the certificate without extra newlines
tpm_certificate = f"-----BEGIN CERTIFICATE-----\n{tpm_certificate}\n-----END CERTIFICATE-----\n'"
gek_public_key = f"-----BEGIN PUBLIC KEY-----\n{gek_public_key}\n-----END PUBLIC KEY-----\n'"

# Append processed data
converted_data.append([
row['Hardware Model'].strip(),
row['Hardware Serial Number'].strip(),
tpm_certificate,
gek_public_key,
"" # Empty UUID field
])

# Write the combined output file
with open(output_file, mode='w', encoding='utf-8', newline='') as outfile:
writer = csv.writer(outfile, quoting=csv.QUOTE_MINIMAL)
# Write the header
writer.writerow(["Model", "Serial", "EK Certificate", "GEK Public Key", "UUID"])
# Write the processed data
writer.writerows(converted_data)

print(f"File converted and saved as {output_file}")

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