Reading a collection of lines

readlines() collects the remaining lines into an independent list[str], keeping their translated newlines. At EOF it returns an empty list. Failures release the partial list, but may have consumed input. For large or untrusted files, bounded readline(count) lets you control memory use instead.

def demo() -> Result[list[str], IoError]:
    write_text("collection.txt", "first\r\n\nlast")?
    with open("collection.txt")? as file:
        return file.readlines()
def main() -> Result[(), IoError]:
    print(demo()?)?
    Ok(())

["first\n", "\n", "last"]

writelines(lines) writes a list[str] without consuming it. It inserts no newlines: include them in the strings when wanted. The operation returns Result[(), IoError]; an error may leave a partially written file.

def demo() -> Result[(), AllocError | IoError]:
    lines = ["one\n", "two\n"]?
    with open("written.txt", "w")? as file:
        file.writelines(lines)?
    print(len(lines))?
    with open("written.txt")? as file:
        print(file.readlines()?)?
    Ok(())
def main() -> Result[(), AllocError | IoError]:
    demo()?
    Ok(())

2
["one\n", "two\n"]