Modern Python Standard Library Cookbook

How it works...

safe_open relies on tempfile to create a new file where the write operations actually happen. Any time we write to f in our context, we are actually writing to the temporary file.

Then, only when the context exists (exc_type is none in safe_open.__exit__), we actually swap the old file with the new one we just wrote, using os.rename.

If everything works as expected, we should have the new file with all its content updated.

If any of the steps fails, we just write some or no data to a temporary file and get rid of it through os.unlink.

Our previous file, in this case, was never touched and thus still retains its previous state.