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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 get_concatenated_pdf_from_disk(filenames: Iterable[str], start_recto: bool = True) -> bytes: """ Concatenates PDFs from disk and returns them as an in-memory binary PDF. Args: filenames: iterable of filenames of PDFs to concatenate start_recto: start a new right-hand page for each new PDF? Returns: concatenated PDF, as ``bytes`` """

    # http://stackoverflow.com/questions/17104926/pypdf-merging-multiple-pdf-files-into-one-pdf  # noqa
    # https://en.wikipedia.org/wiki/Recto_and_verso
    if start_recto:
        writer = PdfFileWriter()
        for filename in filenames:
            if filename:
                if writer.getNumPages() % 2 != 0:
                    writer.addBlankPage()
                writer.appendPagesFromReader(
                    PdfFileReader(open(filename, 'rb')))
        return pdf_from_writer(writer)
    else:
        merger = PdfFileMerger()
        for filename in filenames:
            if filename:
                merger.append(open(filename, 'rb'))
        return pdf_from_writer(merger)