Flush and synchronize writes

write(text) returns a character count and preserves exact bytes, including newlines. flush() flushes runtime buffers; files are currently unbuffered. Use sync() when you need to request that the OS synchronize file contents and metadata. Closing or flushing alone does not make that request.

Run this in a scratch directory: it replaces plenty-stream.txt.

def write_example() -> Result[(), IoError]:
    with open("plenty-stream.txt", "w")? as file:
        print(file.write("hello\n")?)?
        file.flush()?
        file.sync()?
        file.close()?
    with open("plenty-stream.txt", "a")? as file:
        file.write("goodbye\n")?
    Ok(())

def main() -> Result[(), IoError]:
    write_example()?
    Ok(())

6

Explicit close lets you propagate its error. Context exit then closes the already closed owner harmlessly. Writing can leave a prefix after an OS error, and append calls are not guaranteed to be atomic records across processes. Synchronization still follows your filesystem’s durability rules.