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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"`importlib.abc.Traversable.read_text()` incompatible with `importlib.resources._functional.read_text()` usage (Python 3.13)","articleBody":"# Bug report\r\n\r\n### Bug description:\r\n\r\nI'm writing a custom importer and discovered that the function signature for `importlib.abc.Traversable.read_text()` is incompatible with the usage in `importlib.resources._functional.read_text()`, specifically on Python 3.13.\r\n\r\n1. `importlib.abc.Traversable.read_text()` is a concrete method; its implementation calls the `.open()` method, which is an abstract method that must be implemented. The expectation is therefore that implementing `.open()` in a Traversable subclass is sufficient for `.read_text()` to work.\r\n\r\n   Note below that the `.read_text()` method is not marked as abstract, and includes only one parameter: `encoding`:\r\n\r\n   https://github.com/python/cpython/blob/30aeb00d367d0cc9e5a7603371636cddea09f1c0/Lib/importlib/resources/abc.py#L84-L90\r\n\r\n2. Application code that attempts to read a package resource, like `importlib.resources.read_text(module, \"resource.txt\")` ultimately leads to a call to `importlib.resources._functional.read_text()`, which attempts to call the `.read_text()` method of a Traversable subclass, but includes an `errors` parameter that doesn't exist in Traversable's default concrete method:\r\n\r\n   https://github.com/python/cpython/blob/30aeb00d367d0cc9e5a7603371636cddea09f1c0/Lib/importlib/resources/_functional.py#L28-L32\r\n\r\n3. Consequently, it appears to be necessary for all Traversable subclasses to not only re-implement its concrete `.read_text()` method, but also to override its signature.\r\n\r\nI think that the Traversable `.read_text()` method signature, and the call site in `importlib.resources._functional.read_text()`, need to align with each other.\r\n\r\n**_I'd like to submit a PR for this!_** However, I would like confirmation that an `errors` parameter should be added to the `Traversable.read_text()` method.\r\n\r\nNote that adding an `errors` parameter was previously discussed in #88368.\r\n\r\n## Demonstration of TypeError bug\r\n\r\n```python\r\nimport io\r\nimport sys\r\nimport typing\r\nimport pathlib\r\nimport types\r\nimport importlib.abc\r\nimport importlib.machinery\r\nimport importlib.metadata\r\nimport importlib.resources.abc\r\n\r\n\r\nclass ExampleFinder(importlib.abc.MetaPathFinder):\r\n    def find_spec(\r\n        self,\r\n        fullname: str,\r\n        path: typing.Sequence[str] | None,\r\n        target: types.ModuleType | None = None,\r\n    ) -\u003e importlib.machinery.ModuleSpec | None:\r\n        if fullname != \"demonstrate_error\":\r\n            return None\r\n\r\n        print(f\"ExampleFinder.find_spec('{fullname}')\")\r\n        spec = importlib.machinery.ModuleSpec(\r\n            name=fullname,\r\n            loader=ExampleLoader(),\r\n            is_package=True,\r\n        )\r\n        return spec\r\n\r\n\r\nsys.meta_path.append(ExampleFinder())\r\n\r\n\r\nclass ExampleLoader(importlib.abc.Loader):\r\n    def exec_module(self, module: types.ModuleType) -\u003e None:\r\n        print(f\"ExampleLoader.exec_module({module})\")\r\n        exec(\"\", module.__dict__)\r\n\r\n    def get_resource_reader(self, fullname: str) -\u003e \"ExampleTraversableResources\":\r\n        print(f\"ExampleLoader.get_resource_reader('{fullname}')\")\r\n        return ExampleTraversableResources(fullname)\r\n\r\n\r\nclass ExampleTraversableResources(importlib.resources.abc.TraversableResources):\r\n    def __init__(self, fullname: str) -\u003e None:\r\n        self.fullname = fullname\r\n\r\n    def files(self) -\u003e \"ExampleTraversable\":\r\n        print(\"ExampleTraversableResources.files()\")\r\n        return ExampleTraversable(self.fullname)\r\n\r\n\r\n# ----------------------------------------------------------------------------\r\n# ExampleTraversable implements all five of the Traversable abstract methods.\r\n# Specifically, it is expected that implementing `.open()` will be sufficient,\r\n# but this will not be the case.\r\n#\r\n\r\nclass ExampleTraversable(importlib.resources.abc.Traversable):\r\n    def __init__(self, path: str):\r\n        self._path = path\r\n\r\n    def iterdir(self) -\u003e typing.Iterator[\"ExampleTraversable\"]:\r\n        yield ExampleTraversable(\"resource.txt\")\r\n\r\n    def is_dir(self) -\u003e bool:\r\n        return False\r\n\r\n    def is_file(self) -\u003e bool:\r\n        return True\r\n\r\n    def open(self, mode='r', *args, **kwargs) -\u003e typing.IO[typing.AnyStr]:\r\n        return io.StringIO(\"Nice! The call to .read_text() succeeded!\")\r\n\r\n    # Uncomment this `.read_text()` method to make `.read_text()` calls work.\r\n    # It overrides the `Traversable.read_text()` signature.\r\n    #\r\n    # def read_text(self, encoding: str | None, errors: str | None) -\u003e str:\r\n    #     print(f\"ExampleTraversable.read_text('{encoding}', '{errors}')\")\r\n    #     return str(super().read_text(encoding))\r\n\r\n    @property\r\n    def name(self) -\u003e str:\r\n        return pathlib.PurePosixPath(self._path).name\r\n\r\n\r\n# -------------------------------------------------------------------------------\r\n# Everything above allows us to import this hard-coded module\r\n# and demonstrate a TypeError lurking in the Traversable.read_text() signature.\r\n#\r\n\r\nimport demonstrate_error\r\n\r\n\r\n# The next line will raise a TypeError.\r\n# `importlib/resources/_functional.py:read_text()` calls `Traversable.read_text()`\r\n# with an `errors` argument that is not supported by the default concrete method.\r\nprint(importlib.resources.read_text(demonstrate_error, \"resource.txt\"))\r\n```\r\n\r\n### CPython versions tested on:\r\n\r\n3.13\r\n\r\n### Operating systems tested on:\r\n\r\nLinux","author":{"url":"https://github.com/kurtmckee","@type":"Person","name":"kurtmckee"},"datePublished":"2024-11-19T13:28:01.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":13},"url":"https://github.com/127012/cpython/issues/127012"}