code: def get_concatenated_pdf_in_memory(
          pdf_plans: Iterable[PdfPlan],
          start_recto: bool = True) -> bytes:
      
      writer = PdfFileWriter()
      for pdfplan in pdf_plans:
          pdfplan.add_to_writer(writer, start_recto=start_recto)
      return pdf_from_writer(writer)
docs: Concatenates PDFs and returns them as an in-memory binary PDF.
  
      Args:
          pdf_plans: iterable of :class:`PdfPlan` objects
          start_recto: start a new right-hand page for each new PDF?
  
      Returns:
          concatenated PDF, as ``bytes``