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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 combine_pdf_as_bytes(pdfs: List[BytesIO]) -> bytes: """Combine PDFs and return a byte-string with the result. Arguments --------- pdfs A list of BytesIO representations of PDFs """

    writer = PdfWriter()
    for pdf in pdfs:
        writer.addpages(PdfReader(pdf).pages)
    bio = BytesIO()
    writer.write(bio)
    bio.seek(0)
    output = bio.read()
    bio.close()
    return output