如何在某些行号之后覆盖/附加行？

Question

I am having a program that write to file in zip format.

 with gzip.open(filename, "at") as jsonfile:
      jsonfile.write(my_json+"\n")

my problem is: if the process stop I write 200 lines instead of 500 (the total). my desire is: I want to overwite those 200 lines when running the program again, but those line are not alone (there is more text previous to the use of the program) and add the rest (300). I know in which line I have to write ( for example, my program started appending text in line 1000)... Is there any method to do this, like:

 with gzip.open(filename, "at") as jsonfile:
      jsonfile.write(my_json+"\n", append_text_after_this_line=="1000")

So I ended with a file with 1500 lines instead of 1700 with 200 lines duplicated.

Answer 1

there are different solutions to your problem

You can count how many lines you have already added to your file, for example:

lines = 0
with gzip.open(filename, "rt") as f:
    for lines, _ in enumerate(f, 1): pass

duplicated_lines = lines - append_after

with gzip.open(filename, "at") as jsonfile:
    remaining_json = '\n'.join(my_json.split('\n')[duplicated_lines:])
    jsonfile.write(remaining_json + "\n")