Nifi: Execute script creating a locked text file

Hi. I am trying to write a text file from execute script with python. Whenever the processor executes, it creates a locked text file. How can I overcome this problem?

Following is the code

from time import gmtime, strftime
import datetime

now = datetime.datetime.now()
current_time = now.strftime("%H:%M:%S")

with open('**path to directory**/time.txt', "a") as f:
current_time = str(current_time) + ('\n')
f.write(current_time)
f.close()