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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _summarize_doc(doc, length=60):
 r"""Parse out a short one line summary from the given doclines. "doc" is the doc string to summarize. "length" is the max length for the summary 'this function does this' 'this function does this and that' 'this function does this' """

    import re
    if doc is None:
        return ""
    assert length > 3, "length <= 3 is absurdly short for a doc summary"
    doclines = doc.strip().splitlines(0)
    if not doclines:
        return ""

    summlines = []
    for i, line in enumerate(doclines):
        stripped = line.strip()
        if not stripped:
            break
        summlines.append(stripped)
        if len(''.join(summlines)) >= length:
            break

    summary = ' '.join(summlines)
    if len(summary) > length:
        summary = summary[:length - 3] + "..."
    return summary