[3.9] bpo-40924: Revert "bpo-39791 native hooks for importlib.resources.files (GH-20576)" (#20760)

This reverts commit 9cf1be46e3 due to
https://bugs.python.org/issue40924.

Lib/importlib/resources.py

@@ -1,13 +1,15 @@
 import os
 
+from . import abc as resources_abc
 from . import _common
-from ._common import as_file, files
+from ._common import as_file
 from contextlib import contextmanager, suppress
+from importlib import import_module
 from importlib.abc import ResourceLoader
 from io import BytesIO, TextIOWrapper
 from pathlib import Path
 from types import ModuleType
-from typing import ContextManager, Iterable, Union
+from typing import ContextManager, Iterable, Optional, Union
 from typing import cast
 from typing.io import BinaryIO, TextIO
 
@@ -31,11 +33,60 @@ Package = Union[str, ModuleType]
 Resource = Union[str, os.PathLike]
 
 
+def _resolve(name) -> ModuleType:
+    """If name is a string, resolve to a module."""
+    if hasattr(name, '__spec__'):
+        return name
+    return import_module(name)
+
+
+def _get_package(package) -> ModuleType:
+    """Take a package name or module object and return the module.
+
+    If a name, the module is imported.  If the resolved module
+    object is not a package, raise an exception.
+    """
+    module = _resolve(package)
+    if module.__spec__.submodule_search_locations is None:
+        raise TypeError('{!r} is not a package'.format(package))
+    return module
+
+
+def _normalize_path(path) -> str:
+    """Normalize a path by ensuring it is a string.
+
+    If the resulting string contains path separators, an exception is raised.
+    """
+    parent, file_name = os.path.split(path)
+    if parent:
+        raise ValueError('{!r} must be only a file name'.format(path))
+    return file_name
+
+
+def _get_resource_reader(
+        package: ModuleType) -> Optional[resources_abc.ResourceReader]:
+    # Return the package's loader if it's a ResourceReader.  We can't use
+    # a issubclass() check here because apparently abc.'s __subclasscheck__()
+    # hook wants to create a weak reference to the object, but
+    # zipimport.zipimporter does not support weak references, resulting in a
+    # TypeError.  That seems terrible.
+    spec = package.__spec__
+    if hasattr(spec.loader, 'get_resource_reader'):
+        return cast(resources_abc.ResourceReader,
+                    spec.loader.get_resource_reader(spec.name))
+    return None
+
+
+def _check_location(package):
+    if package.__spec__.origin is None or not package.__spec__.has_location:
+        raise FileNotFoundError(f'Package has no location {package!r}')
+
+
 def open_binary(package: Package, resource: Resource) -> BinaryIO:
     """Return a file-like object opened for binary reading of the resource."""
-    resource = _common.normalize_path(resource)
-    package = _common.get_package(package)
-    reader = _common.get_resource_reader(package)
+    resource = _normalize_path(resource)
+    package = _get_package(package)
+    reader = _get_resource_reader(package)
     if reader is not None:
         return reader.open_resource(resource)
     absolute_package_path = os.path.abspath(
@@ -89,6 +140,13 @@ def read_text(package: Package,
         return fp.read()
 
 
+def files(package: Package) -> resources_abc.Traversable:
+    """
+    Get a Traversable resource from a package
+    """
+    return _common.from_package(_get_package(package))
+
+
 def path(
         package: Package, resource: Resource,
         ) -> 'ContextManager[Path]':
@@ -100,18 +158,17 @@ def path(
     raised if the file was deleted prior to the context manager
     exiting).
     """
-    reader = _common.get_resource_reader(_common.get_package(package))
+    reader = _get_resource_reader(_get_package(package))
     return (
         _path_from_reader(reader, resource)
         if reader else
-        _common.as_file(
-            _common.files(package).joinpath(_common.normalize_path(resource)))
+        _common.as_file(files(package).joinpath(_normalize_path(resource)))
         )
 
 
 @contextmanager
 def _path_from_reader(reader, resource):
-    norm_resource = _common.normalize_path(resource)
+    norm_resource = _normalize_path(resource)
     with suppress(FileNotFoundError):
         yield Path(reader.resource_path(norm_resource))
         return
@@ -125,9 +182,9 @@ def is_resource(package: Package, name: str) -> bool:
 
     Directories are *not* resources.
     """
-    package = _common.get_package(package)
-    _common.normalize_path(name)
-    reader = _common.get_resource_reader(package)
+    package = _get_package(package)
+    _normalize_path(name)
+    reader = _get_resource_reader(package)
     if reader is not None:
         return reader.is_resource(name)
     package_contents = set(contents(package))
@@ -143,8 +200,8 @@ def contents(package: Package) -> Iterable[str]:
     not considered resources.  Use `is_resource()` on each entry returned here
     to check if it is a resource or not.
     """
-    package = _common.get_package(package)
-    reader = _common.get_resource_reader(package)
+    package = _get_package(package)
+    reader = _get_resource_reader(package)
     if reader is not None:
         return reader.contents()
     # Is the package a namespace package?  By definition, namespace packages