import re
p = re.compile(r'.{0,50}(?:\s|$)')
test_str = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris risus orci, varius eu orci non, tristique faucibus sapien. Suspendisse eu eros et quam viverra hendrerit in eu enim. Etiam vehicula imperdiet placerat. Sed rhoncus ipsum sit amet pellentesque laoreet. Nunc sodales fringilla lacus. Praesent urna sem, sodales id sagittis non, accumsan non massa. Nulla ultricies fermentum diam, quis imperdiet eros maximus vel. Morbi at arcu ante. Nulla eget augue id mi semper rhoncus.Praesent varius lacinia tristique. Aliquam non turpis laoreet, facilisis ante in, tincidunt sapien. Morbi et metus in eros consequat ultricies ut vitae augue. Praesent vitae hendrerit massa. Integer feugiat lacus mi. Ut et arcu quis ligula cursus congue. Suspendisse potenti. In lacus magna, sodales a sem auctor, rhoncus vehicula quam. Aliquam ac elit at justo semper ultrices. Praesent pellentesque purus non neque consectetur tempus. Nunc ultricies sollicitudin dignissim. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae; Praesent non neque ex. Vivamus cursus luctus felis, non tempus ipsum. Pellentesque fringilla risus non nibh porta, viverra blandit augue vulputate. Curabitur tristique pretium eleifend. Nulla dolor nisl, hendrerit eu ornare a, rhoncus et felis. Donec non ultricies ipsum. Mauris ac urna id metus maximus condimentum dictum sed elit. Nunc et metus porttitor."
subst = r"\g<0>\n"
result = p.sub(subst, test_str)
print(result)

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