Use as_file for a package resource path

A Traversable package resource can be read directly with methods such as read_text(), but some APIs accept only a real pathlib.Path. importlib.resources.as_file() bridges that gap. Give it a Traversable, normally obtained from files(package).joinpath(name), and use the resulting path inside a with statement.

The temporary package in this example contains message.txt with the text hello. files(package).joinpath("message.txt") identifies that resource without assuming an installation directory. Within as_file(resource), the code asserts that the supplied object is a file, reads its UTF-8 content through the provided Path, and prints message.txt: hello. The post-context assertion preserves the value read while ensuring the output does not depend on a machine-specific temporary location.

A resource may already be a normal file, as it is in this fixture, or it may need extraction before a filesystem-only consumer can use it. When extraction is needed, as_file() cleans up the temporary materialization after the context exits. Therefore, do not retain the yielded path, pass it to work that outlives the with block, or print it as stable configuration. Prefer the Traversable reading methods when an actual path is unnecessary. as_file() supports file resources from Python 3.9; support for directory Traversable objects was added in Python 3.12.

AI assistance disclosure: this article was drafted with AI assistance.

See the official importlib.resources documentation.

import importlib
import importlib.resources as resources
import sys
from pathlib import Path
from tempfile import TemporaryDirectory

with TemporaryDirectory() as directory:
    package_dir = Path(directory) / "message_package"
    package_dir.mkdir()
    (package_dir / "__init__.py").write_text("", encoding="utf-8")
    (package_dir / "message.txt").write_text("hello", encoding="utf-8")

    sys.path.insert(0, directory)
    try:
        importlib.invalidate_caches()
        package = importlib.import_module("message_package")
        resource = resources.files(package).joinpath("message.txt")

        with resources.as_file(resource) as path:
            assert path.is_file()
            text = path.read_text(encoding="utf-8")

        assert text == "hello"
        print(f"message.txt: {text}")
    finally:
        sys.path.remove(directory)
        sys.modules.pop("message_package", None)
message.txt: hello

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