This isn't right for pre-3.14 versions - the version = line fails because there's no a.value.value on older versions. Something like this works (tested on 2.7 and 3.11-3.14):

version = None
with open(join(here, "html5lib", "__init__.py"), "rb") as init_file:
    t = ast.parse(init_file.read(), filename="__init__.py", mode="exec")
    assert isinstance(t, ast.Module)
    assignments = filter(lambda x: isinstance(x, ast.Assign), t.body)
    for a in assignments:
        if (len(a.targets) == 1 and
                isinstance(a.targets[0], ast.Name) and
                a.targets[0].id == "__version__"):
            if hasattr(ast, "Str") and isinstance(a.value, ast.Str):
                version = a.value.s
            elif (hasattr(ast, "Constant")
                  and isinstance(a.value, ast.Constant)
                  and isinstance(a.value.value, str)):
                version = a.value.value
assert version is not None

Thanks! Updated the PR.

Could you fix appveyor? For example the flake8 formatting.
https://ci.appveyor.com/project/gsnedders/html5lib-python/builds/52890634

setup.py declares python_requires >= 2.7, but Python 3.13 is not tested in appveyor.

Python 3.7 is EOL since 2023-06-27, when will it be allowed to not stay compatible anymore?

py --list
-V:3.8 Python 3.8 (64-bit)
No suitable Python runtime found

Python 2.7 is EOL since 2020-01-01, when will it be allowed to not stay compatible anymore?
Microsoft Visual C++ 9.0 is 15 years old and not available anymore officially of course.

running build_ext
building 'lxml.etree' extension
error: Microsoft Visual C++ 9.0 is required. Get it from http://aka.ms/vcpython27

https://web.archive.org/web/20190720195601/http://www.microsoft.com/en-us/download/confirmation.aspx?id=44266