ROB: page._get_fonts() gives KeyError: '/BaseFont'

[MartinThoma]

I wanted to get the fonts of a page and got a KeyError: '/BaseFont'

Environment

Which environment were you using when you encountered the problem?

$ python -m platform
Linux-5.4.0-166-generic-x86_64-with-glibc2.31

$ python -c "import pypdf;print(pypdf._debug_versions)"
pypdf==3.17.0, crypt_provider=('cryptography', '41.0.4'), PIL=10.0.0

Code + PDF

This is a minimal, complete example that shows the issue:

from pypdf import PdfReader

reader = PdfReader('missing-base-font.pdf')
page = reader.pages[0]
page._get_fonts()

The PDF:
missing-base-font.pdf

Traceback

This is the complete Traceback I see:

Traceback (most recent call last):
  File "/home/moose/Documents/foo.py", line 5, in <module>
    page._get_fonts()
  File "/home/moose/Github/py-pdf/pypdf/pypdf/_page.py", line 2349, in _get_fonts
    fonts, embedded = _get_fonts_walk(obj, fonts, embedded)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/moose/Github/py-pdf/pypdf/pypdf/_page.py", line 2645, in _get_fonts_walk
    process_font(f)
  File "/home/moose/Github/py-pdf/pypdf/pypdf/_page.py", line 2635, in process_font
    emb.add(cast(str, f["/BaseFont"]))
                      ~^^^^^^^^^^^^^
  File "/home/moose/Github/py-pdf/pypdf/pypdf/generic/_data_structures.py", line 333, in __getitem__
    return dict.__getitem__(self, key).get_object()
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
KeyError: '/BaseFont'

[MartinThoma]

@pubpub-zz I would replace

            # the list comprehension ensures there is FontFile
            emb.add(cast(str, f["/BaseFont"]))

in _page.py by

            if (...) and "/BaseFont" in f:
                emb.add(cast(str, f["/BaseFont"]))

That would at least make the exception go away. But I don't know why we have that big if-block. I guess there is something else wrong?

[pubpub-zz]

The problem here is that the font is a Type 3 that does not contains /BaseFont property.
I would propose this mod:

emb.add(cast(str, f.get("/BaseFont","("+f["/SubType"]+")")))

about the big if block, so far from I remember I've written it as a list of if but ruff/black optimized it