Read a file in chunks of [length to the first newline after length chars after previous block]. There may be an easier solution...

read_multiline_file_in_chunks_of_whole_lines.py

import io

def read_in_chunks_of_whole_lines(file, length=1024*1024):
    """Read a file in blocks of length bytes, up to the next newline."""
    tail = ""
    with open(file, "r") as f:
        while True:
            chunk = tail + f.read(length)
            if not chunk:
                return
            
            while True:
                part = f.read(128 + length//8)
                idx = part.find("\n")
                if idx >= 0:
                    chunk += part[:idx]
                    tail = part[idx:]
                    yield io.StringIO(chunk)
                    break
                else:
                    chunk += part