`TypeError` raised when creating a `Codec` for a class with a `ClassVar[LiteralString]`

[JesseTG]

Thanks for this library! It's helped me a lot with some repetitive tasks for a project I'm working on.

I did find a bug that I'd like to report, however. Specifically, typelib raises an error when constructing a Codec for a type that has a ClassVar[LiteralString]. This issue occurs with Python 3.13.7 on Windows 10, with typelib 0.2.0.

Here's a stack trace:

  File "D:\Code\Contributions\libretro-database\.venv\python313\Lib\site-packages\typelib\py\inspection.py", line 663, in isdatetimetype
    return builtins.issubclass(origin(obj), datetime.datetime)
           ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Code\Contributions\libretro-database\.venv\python313\Lib\site-packages\typelib\marshals\api.py", line 70, in _get_unmarshaller
    if check(node.unwrapped):  # type: ignore[arg-type]
       ~~~~~^^^^^^^^^^^^^^^^
  File "D:\Code\Contributions\libretro-database\.venv\python313\Lib\site-packages\typelib\marshals\api.py", line 56, in marshaller
    context[node.type] = _get_unmarshaller(node, context=context)
                         ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\Code\Contributions\libretro-database\.venv\python313\Lib\site-packages\typelib\codecs.py", line 57, in codec
    marshal = marshaller or marshals.marshaller(t=t)
                            ~~~~~~~~~~~~~~~~~~~^^^^^
  File "D:\Code\Contributions\libretro-database\scripts\igdb.py", line 1359, in <module> (Current frame)
    GameTupleCodec: typelib.Codec[tuple[Game, ...]] = typelib.codec(tuple[Game, ...])
                                                      ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
  File "D:\Code\Contributions\libretro-database\scripts\match.py", line 26, in <module>
    from igdb import load_game_file
  File "C:\Python313\Lib\runpy.py", line 88, in _run_code
    exec(code, run_globals)
  File "C:\Python313\Lib\runpy.py", line 198, in _run_module_as_main
    return _run_code(code, main_globals, None,
TypeError: issubclass() arg 1 must be a class

And here's a minimal reproduction:

import dataclasses
import typelib

from typing import ClassVar, LiteralString

@dataclasses.dataclass
class Game:
    id: int

    __table__: ClassVar[LiteralString] = "<hardcoded SQL statement>"

GameTupleCodec: typelib.Codec[tuple[Game, ...]] = typelib.codec(tuple[Game, ...])

You can see the full code here. To run it you'll need to install the requirements.txt in that branch, then you can either import igdb.py as a module or run it as a script.

A workaround is to replace the LiteralString with a str.

[seandstewart]

Hey @JesseTG -

Thanks for reporting this issue! This is a missing feature in the typelib.py.inspection.origin function:

python-typelib/src/typelib/py/inspection.py

Lines 90 to 131 in 216242b

	def origin(annotation: tp.Any) -> tp.Any:
	"""Get the highest-order 'origin'-type for a given type definition.
	Tip:
	For the purposes of this library, if we can resolve to a builtin type, we will.
	Examples:
	>>> from typelib.py import inspection
	>>> from typing import Dict, Mapping, NewType, Optional
	>>> origin(Dict)
	<class 'dict'>
	>>> origin(Mapping)
	<class 'dict'>
	>>> Registry = NewType('Registry', Dict)
	>>> origin(Registry)
	<class 'dict'>
	>>> class Foo: ...
	...
	>>> origin(Foo)
	<class 'typelib.Foo'>
	"""
	# Resolve custom NewTypes.
	actual = resolve_supertype(annotation)
	# Unwrap optional/classvar
	if isclassvartype(actual):
	a = args(actual)
	actual = a[0] if a else actual
	if istypealiastype(actual):
	actual = actual.__value__
	actual = tp.get_origin(actual) or actual
	# provide defaults for generics
	if not isbuiltintype(actual):
	actual = _check_generics(actual)
	if iscallable(actual):
	actual = tp.Callable
	return actual

Can just update the GENERIC_TYPE_MAP to include the LiteralString. Would need to update typelib.py.compat to provide a safe import of LiteralString with a default of str, then add it to the mapping like so: compat.LiteralString: str.