Overwrite part of a large file in Python

Question

I am writing a bit torrent client and allocate space on hard drive for each file I have to download.

File can be huge and I want to overwrite some piece of it without deleting all content.

I read some other answers, but they suggest creating a temporary space and then copying changes back. That would be too heavy process.

I am sure there must be some utility.

Answer 1

Since you are talking about a download file, you should consider the storage of downloaded data in a temporary file(chunks). Refer : streaming & text-file

If I read you question (without python), I would say you could use OS specific commands to overwrite parts of a file.

For example in Linux, use sed or awk . Refer : Inserting-a-line-in-a-file-at-a-specific-location

Answer 2

I found a solution, using OS (Linux) specific system call:

fd = os.open(path, os.O_WRONLY)
os.lseek(fd, offset, os.SEEK_SET)
os.write(fd, piece)
os.close(fd)

This did overwrite file without nullifying it. But when had:

with open(path, 'wb') as file:
    file.seek(offset)
    file.write(piece)

It was deleting all other content.

Program is not portable this way but I don't need it to be.