Bug: dataclasses.FrozenInstanceError: cannot assign to field 'glyph_id', deepcopy issue, section_title_styles, add_font

[Samu1808]

Describe the bug

I encountered a weird issue in the new version 2.7.5 with 2.7.4 everything works fine.

Error details

Traceback (most recent call last):
  File "/path/to/venv/bin/sil-run-test", line 33, in <module>
    sys.exit(load_entry_point('sil-tests', 'console_scripts', 'sil-run-test')())
  File "/path/to/sil-tests/sil_tests/main/cli.py", line 62, in main
    print_results(ResultsList, args.pdf_output)
  File "/path/to/sil-tests/sil_tests/pdf_results/pdf_results.py", line 159, in print_results
    pdf.start_section("Test Results", 0)
  File "/path/to/venv/lib/python3.9/site-packages/fpdf/fpdf.py", line 217, in wrapper
    return fn(self, *args, **kwargs)
  File "/path/to/venv/lib/python3.9/site-packages/fpdf/fpdf.py", line 4642, in start_section
    with self.offset_rendering() as pdf:
  File "/usr/lib64/python3.9/contextlib.py", line 119, in __enter__
    return next(self.gen)
  File "/path/to/venv/lib/python3.9/site-packages/fpdf/fpdf.py", line 4546, in offset_rendering
    recorder = FPDFRecorder(self, accept_page_break=False)
  File "/path/to/venv/lib/python3.9/site-packages/fpdf/recorder.py", line 30, in __init__
    self._initial = deepcopy(self.pdf.__dict__)
  File "/usr/lib64/python3.9/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/usr/lib64/python3.9/copy.py", line 230, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib64/python3.9/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/usr/lib64/python3.9/copy.py", line 230, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib64/python3.9/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/usr/lib64/python3.9/copy.py", line 270, in _reconstruct
    state = deepcopy(state, memo)
  File "/usr/lib64/python3.9/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/usr/lib64/python3.9/copy.py", line 210, in _deepcopy_tuple
    y = [deepcopy(a, memo) for a in x]
  File "/usr/lib64/python3.9/copy.py", line 210, in <listcomp>
    y = [deepcopy(a, memo) for a in x]
  File "/usr/lib64/python3.9/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/usr/lib64/python3.9/copy.py", line 230, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib64/python3.9/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/usr/lib64/python3.9/copy.py", line 270, in _reconstruct
    state = deepcopy(state, memo)
  File "/usr/lib64/python3.9/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/usr/lib64/python3.9/copy.py", line 230, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib64/python3.9/copy.py", line 146, in deepcopy
    y = copier(x, memo)
  File "/usr/lib64/python3.9/copy.py", line 230, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
  File "/usr/lib64/python3.9/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
  File "/usr/lib64/python3.9/copy.py", line 282, in _reconstruct
    setattr(y, key, value)
  File "<string>", line 4, in __setattr__
dataclasses.FrozenInstanceError: cannot assign to field 'glyph_id'

Minimal code
Here is some sample code which lead to this behaviour, note that you need to define the pdf.section_title_styles and import a font the way I did it in order to get the error. It is not a issue with this particular font, I tried others aswell but this did not effect the issue.

import fpdf 

pdf = fpdf.FPDF()
pdf.section_title_styles = [
    fpdf.TitleStyle(font_family="helvetica", font_style="B", font_size_pt=24, b_margin=10),
    fpdf.TitleStyle(font_family="helvetica", font_style="B", font_size_pt=18, b_margin=2, t_margin=4),
    fpdf.TitleStyle(font_family="helvetica", font_style="B", font_size_pt=12, b_margin=1, t_margin=4)
]
pdf.add_font("monospace", "", "SourceCodePro-Regular.ttf")
pdf.add_page()
pdf.start_section("Sample Section", 0)

pdf.output("sample_output.pdf")

Environment

• Operating System: Fedora 34 in a docker container
  • Dockerfile:

FROM fedora:34

RUN dnf install -y gcc make python python-pip python-virtualenv git glibc-devel findutils

• Python version: 3.9.12
• fpdf2 version used: 2.7.5

I have reviewed the release notes for version 2.7.5 but could not identify a specific change that might be related to this issue. Any guidance or resolution would be appreciated. My workaround for now is using the 2.7.4 version.

Thank you!

[andersonhc]

Thanks for reporting the problem @Samu1808
This issue was introduced by #820 because I made Glyph a frozen dataclass. Consequently FPDFRecorder can not use deepcopy on it.
I will open a PR to fix this problem.

[Samu1808]

Oh nice, that was fast :) thanks for your work

[Lucas-C]

This was fixed by @andersonhc in #891