How to write to the beginning of a file when using Python subprocess.call()?

Question

I run the following script:

with open("logfile.txt", 'w') as log_file:
    cmd = path + '/somebinary'
    log_file.write("Running the command: %s\n" % cmd)
    subprocess.call(cmd, shell=True, stdout=log_file, stderr=log_file)

However, the cmd variable gets written to the end of the file and not to the beginning (which I was expecting / hoping for). Can somebody explain to me why and how to prevent this, please?

Answer 1

I came up with an idea to do it this way, maybe you will find it useful.

Input: text.txt

123
lol
stack
overflow

Code

'''First I read the content of existing file and i append the first line of it to the text i want to appear in beginning'''
with open("text.txt", "r") as f:
    existing_lines = f.readlines()
    text_to_append = "Test"
    existing_lines[0] = text_to_append+"\n"+existing_lines[0]
'''And here I wite to the file'''
with open("text.txt", "w") as f:
    f.writelines(existing_lines)

Output: text.txt

Test
123
lol
stack
overflow

You can put anything in the text_to_append as long as its string.