How do i the same header to a python .txt file thats appendeded and created every hour?

I am trying to figure out how to add a header to a .txt file which is a keystroke logger in python. Right now the problem with my code is that my header is displayed after every key is logged. But I need the header to be in the .txt file within its own line above the logged data. Additionally, for each .txt file created I need the header to be the same, but display I different time(I already have a time method for this ) For instance: this is how my .txt file currently looks with my code:

[START OF LOGS]
  *~ Date/Time: Thu Aug 11 10:57:21 2022
 t[START OF LOGS]
  *~ Date/Time: Thu Aug 11 10:57:21 2022
 e[START OF LOGS]
  *~ Date/Time: Thu Aug 11 10:57:21 2022
 s[START OF LOGS]
  *~ Date/Time: Thu Aug 11 10:57:21 2022
 t[START OF LOGS]
  *~ Date/Time: Thu Aug 11 10:57:21 2022

This is how I need the .txt file to be shown. As you can see the header is above the logged data. I also need it to not interfere with the logged data

[START OF LOGS]
  *~ Date/Time: Thu Aug 11 10:57:21 2022
test

Here are the variables used for the Header, it just collects the date and time from the time library

datetime = time.ctime(time.time())
Header = f'[START OF LOGS]\n  *~ Date/Time: {datetime}\n'

this is the function that creates the .txt file. Currently the f.write(Header) is what's giving me the unwanted .txt file(first picture). Would I need to use a different method? I am calling the write_file functiion as a callback.

def write_file(keys):
    with open(log.txt, "a") as f: 
        f.write(Header)
        for key in keys:
            k = str(key).replace("'", "")
            # f.write(str(key)) 
            if k.find("space") >= 0:  
                f.write('\n')
                f.close()