Typing annotations fixed in version.py

[jolaf]

I've run my app under typeguard and it found couple of typing annotation issues that I fix here.

[jolaf]

See also pypa/setuptools#4044

[brettcannon]

Since mypy didn't report any type issues with this code, I wonder if the None checks are actually wrong instead of the type annotations?

[jolaf]

mypy has a very limited capability in reading the real logic of the code, it mostly checks declarations and assignments.
If you check a variable for None, it would not expect you to declare None as a valid value.

typeguard is a runtime checker, it checks what really gets passed into a method.

Under typeguard, simply importing pkg_resources fails like this:

test.py:

from typeguard import install_import_hook
with install_import_hook(('pkg_resources',)):
    import pkg_resources

$ python3 test.py 
Traceback (most recent call last):
  File "test.py", line 3, in <module>
    import pkg_resources
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_importhook.py", line 98, in exec_module
    super().exec_module(module)
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/__init__.py", line 3328, in <module>
    def _initialize_master_working_set():
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/__init__.py", line 3302, in _call_aside
    f(*args, **kwargs)
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/__init__.py", line 3340, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/__init__.py", line 622, in _build_master
    ws = cls()
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/__init__.py", line 615, in __init__
    self.add_entry(entry)
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/__init__.py", line 671, in add_entry
    for dist in find_distributions(entry, True):
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/__init__.py", line 2134, in find_on_path
    for dist in factory(fullpath):
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/__init__.py", line 2199, in distributions_from_metadata
    yield Distribution.from_location(
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/__init__.py", line 2665, in from_location
    return cls(
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/__init__.py", line 2646, in __init__
    self._version = safe_version(version)
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/__init__.py", line 1398, in safe_version
    return str(packaging.version.Version(version))
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/_vendor/packaging/version.py", line 204, in __init__
    pre=_parse_letter_version(match.group("pre_l"), match.group("pre_n")),
  File "/home/jolaf/.local/lib/python3.10/site-packages/pkg_resources/_vendor/packaging/version.py", line 453, in _parse_letter_version
    def _parse_letter_version(
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_functions.py", line 138, in check_argument_types
    check_type_internal(value, annotation, memo)
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_checkers.py", line 764, in check_type_internal
    raise TypeCheckError(f"is not an instance of {qualified_name(origin_type)}")
typeguard.TypeCheckError: argument "letter" (None) is not an instance of str

So, a None gets actually passed as a letter argument.
You can investigate the stack trace (ignoring typeguard lines) and find out how it happens (both match.group() calls in version.py:204 return None).
Maybe it's a bug in the code and letter should never be None.
But without typeguard the code works fine, so I suppose that None is a valid value, and typing annotation should reflect that.

[brettcannon]

But without typeguard the code works fine, so I suppose that None is a valid value, and typing annotation should reflect that.

I don't know if that's necessarily true that typing "should reflect that" as an empty e.g. dict would also work since there's no specific check for None but for false-y values (hence my question of what triggered this).

But since other parameters do look to be expecting None as a possible value, I'm fine with it.

P.S.: I'm assuming typeguard is https://pypi.org/project/typeguard/ .

[jolaf]

Yep, that's right. Thanks!