ENH: Add templateflow._loader to replace pkg_resources

Author: effigies

setup.cfg

@@ -32,6 +32,7 @@ setup_requires =
     wheel
 install_requires =
     pybids >= 0.15.2
+    importlib_resources >= 5.7; python_version < '3.11'
     requests
     tqdm
 test_requires =

templateflow/_loader.py

@@ -0,0 +1,171 @@
+"""Resource loader module
+
+.. autoclass:: Loader
+"""
+from __future__ import annotations
+
+import atexit
+import os
+from contextlib import AbstractContextManager, ExitStack
+from functools import cached_property
+from pathlib import Path
+from types import ModuleType
+from typing import Union
+
+try:
+    from functools import cache
+except ImportError:  # PY38
+    from functools import lru_cache as cache
+
+try:  # Prefer backport to leave consistency to dependency spec
+    from importlib_resources import as_file, files
+except ImportError:
+    from importlib.resources import as_file, files  # type: ignore
+
+try:  # Prefer stdlib so Sphinx can link to authoritative documentation
+    from importlib.resources.abc import Traversable
+except ImportError:
+    from importlib_resources.abc import Traversable
+
+__all__ = ["Loader"]
+
+
+class Loader:
+    """A loader for package files relative to a module
+
+    This class wraps :mod:`importlib.resources` to provide a getter
+    function with an interpreter-lifetime scope. For typical packages
+    it simply passes through filesystem paths as :class:`~pathlib.Path`
+    objects. For zipped distributions, it will unpack the files into
+    a temporary directory that is cleaned up on interpreter exit.
+
+    This loader accepts a fully-qualified module name or a module
+    object.
+
+    Expected usage::
+
+        '''Data package
+
+        .. autofunction:: load_data
+
+        .. automethod:: load_data.readable
+
+        .. automethod:: load_data.as_path
+
+        .. automethod:: load_data.cached
+        '''
+
+        from templateflow._loader import Loader
+
+        load_data = Loader(__package__)
+
+    :class:`~Loader` objects implement the :func:`callable` interface
+    and generate a docstring, and are intended to be treated and documented
+    as functions.
+
+    For greater flexibility and improved readability over the ``importlib.resources``
+    interface, explicit methods are provided to access resources.
+
+    +---------------+----------------+------------------+
+    | On-filesystem | Lifetime       | Method           |
+    +---------------+----------------+------------------+
+    | `True`        | Interpreter    | :meth:`cached`   |
+    +---------------+----------------+------------------+
+    | `True`        | `with` context | :meth:`as_path`  |
+    +---------------+----------------+------------------+
+    | `False`       | n/a            | :meth:`readable` |
+    +---------------+----------------+------------------+
+
+    It is also possible to use ``Loader`` directly::
+
+        from templateflow._loader import Loader
+
+        Loader(other_package).readable('data/resource.ext').read_text()
+
+        with Loader(other_package).as_path('data') as pkgdata:
+            # Call function that requires full Path implementation
+            func(pkgdata)
+
+        # contrast to
+
+        from importlib_resources import files, as_file
+
+        files(other_package).joinpath('data/resource.ext').read_text()
+
+        with as_file(files(other_package) / 'data') as pkgdata:
+            func(pkgdata)
+
+    .. automethod:: readable
+
+    .. automethod:: as_path
+
+    .. automethod:: cached
+    """
+
+    def __init__(self, anchor: Union[str, ModuleType]):
+        self._anchor = anchor
+        self.files = files(anchor)
+        self.exit_stack = ExitStack()
+        atexit.register(self.exit_stack.close)
+        # Allow class to have a different docstring from instances
+        self.__doc__ = self._doc
+
+    @cached_property
+    def _doc(self):
+        """Construct docstring for instances
+
+        Lists the public top-level paths inside the location, where
+        non-public means has a `.` or `_` prefix or is a 'tests'
+        directory.
+        """
+        top_level = sorted(
+            os.path.relpath(p, self.files) + "/"[: p.is_dir()]
+            for p in self.files.iterdir()
+            if p.name[0] not in (".", "_") and p.name != "tests"
+        )
+        doclines = [
+            f"Load package files relative to ``{self._anchor}``.",
+            "",
+            "This package contains the following (top-level) files/directories:",
+            "",
+            *(f"* ``{path}``" for path in top_level),
+        ]
+
+        return "\n".join(doclines)
+
+    def readable(self, *segments) -> Traversable:
+        """Provide read access to a resource through a Path-like interface.
+
+        This file may or may not exist on the filesystem, and may be
+        efficiently used for read operations, including directory traversal.
+
+        This result is not cached or copied to the filesystem in cases where
+        that would be necessary.
+        """
+        return self.files.joinpath(*segments)
+
+    def as_path(self, *segments) -> AbstractContextManager[Path]:
+        """Ensure data is available as a :class:`~pathlib.Path`.
+
+        This method generates a context manager that yields a Path when
+        entered.
+
+        This result is not cached, and any temporary files that are created
+        are deleted when the context is exited.
+        """
+        return as_file(self.files.joinpath(*segments))
+
+    @cache
+    def cached(self, *segments) -> Path:
+        """Ensure data is available as a :class:`~pathlib.Path`.
+
+        Any temporary files that are created remain available throughout
+        the duration of the program, and are deleted when Python exits.
+
+        Results are cached so that multiple calls do not unpack the same
+        data multiple times, but the cache is sensitive to the specific
+        argument(s) passed.
+        """
+        return self.exit_stack.enter_context(as_file(self.files.joinpath(*segments)))
+
+    __call__ = cached