PdfMerger does not merge outlines of pdf documents with single pages about pypdf

[stefan6419846]

PyPDF2 and PdfMerger are deprecated, please move to pypdf.PdfWriter. If the issue still persists, please update your code accordingly.

[fhg-isi]

Switching to PdfWriter did the trick. (Switching from pypdf2 to pypdf and updating pypdf from 3.15.2 to 4.2.0 did not help.)

import os

import matplotlib.pyplot as plt
from pypdf import PdfWriter, PdfReader


def main():

    x = [1, 2, 3, 4, 5]
    y = [2, 4, 6, 8, 10]

    fig, ax = plt.subplots()
    ax.plot(x, y)

    save_pdf_with_outline_title(fig, 'first.pdf', 'first_outline_title')

    save_pdf_with_outline_title(fig, 'second.pdf', 'second_outline_title')

    writer = PdfWriter()
    first_pdf = PdfReader('first.pdf')
    writer.append(first_pdf, import_outline=True)

    second_pdf = PdfReader('second.pdf')
    writer.append(second_pdf, import_outline=True)

    writer.write('result.pdf')


def save_pdf_with_outline_title(graph, file_path, outline_title):
    temp_file_path = file_path.replace('.pdf', '_temp.pdf')
    graph.savefig(temp_file_path, bbox_inches='tight')

    writer = PdfWriter()
    temp_pdf = PdfReader(temp_file_path)
    writer.append(temp_pdf, outline_item=outline_title)

    writer.write(file_path)
    os.remove(temp_file_path)


if __name__ == '__main__':
    main()