diff --git a/.gitattributes b/.gitattributes
index fd303806dac..68566e89924 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -28,6 +28,7 @@ Lib/test/test_email/data/*.txt -text
 Lib/test/xmltestdata/* -text
 Lib/test/coding20731.py -text
 Lib/test/test_importlib/data01/* -text
+Lib/test/test_importlib/namespacedata01/* -text
 
 # CRLF files
 *.bat text eol=crlf
diff --git a/Lib/importlib/_adapters.py b/Lib/importlib/_adapters.py
index eedde49dd03..9907b148b39 100644
--- a/Lib/importlib/_adapters.py
+++ b/Lib/importlib/_adapters.py
@@ -1,4 +1,5 @@
 from contextlib import suppress
+from io import TextIOWrapper
 
 from . import abc
 
@@ -25,32 +26,119 @@ class TraversableResourcesLoader:
         self.spec = spec
 
     def get_resource_reader(self, name):
-        return DegenerateFiles(self.spec)._native()
+        return CompatibilityFiles(self.spec)._native()
 
 
-class DegenerateFiles:
+def _io_wrapper(file, mode='r', *args, **kwargs):
+    if mode == 'r':
+        return TextIOWrapper(file, *args, **kwargs)
+    elif mode == 'rb':
+        return file
+    raise ValueError(
+        "Invalid mode value '{}', only 'r' and 'rb' are supported".format(mode)
+    )
+
+
+class CompatibilityFiles:
     """
     Adapter for an existing or non-existant resource reader
-    to provide a degenerate .files().
+    to provide a compability .files().
     """
 
-    class Path(abc.Traversable):
+    class SpecPath(abc.Traversable):
+        """
+        Path tied to a module spec.
+        Can be read and exposes the resource reader children.
+        """
+
+        def __init__(self, spec, reader):
+            self._spec = spec
+            self._reader = reader
+
+        def iterdir(self):
+            if not self._reader:
+                return iter(())
+            return iter(
+                CompatibilityFiles.ChildPath(self._reader, path)
+                for path in self._reader.contents()
+            )
+
+        def is_file(self):
+            return False
+
+        is_dir = is_file
+
+        def joinpath(self, other):
+            if not self._reader:
+                return CompatibilityFiles.OrphanPath(other)
+            return CompatibilityFiles.ChildPath(self._reader, other)
+
+        @property
+        def name(self):
+            return self._spec.name
+
+        def open(self, mode='r', *args, **kwargs):
+            return _io_wrapper(self._reader.open_resource(None), mode, *args, **kwargs)
+
+    class ChildPath(abc.Traversable):
+        """
+        Path tied to a resource reader child.
+        Can be read but doesn't expose any meaningfull children.
+        """
+
+        def __init__(self, reader, name):
+            self._reader = reader
+            self._name = name
+
         def iterdir(self):
             return iter(())
 
-        def is_dir(self):
-            return False
+        def is_file(self):
+            return self._reader.is_resource(self.name)
 
-        is_file = exists = is_dir  # type: ignore
+        def is_dir(self):
+            return not self.is_file()
 
         def joinpath(self, other):
-            return DegenerateFiles.Path()
+            return CompatibilityFiles.OrphanPath(self.name, other)
 
+        @property
         def name(self):
-            return ''
+            return self._name
 
-        def open(self):
-            raise ValueError()
+        def open(self, mode='r', *args, **kwargs):
+            return _io_wrapper(
+                self._reader.open_resource(self.name), mode, *args, **kwargs
+            )
+
+    class OrphanPath(abc.Traversable):
+        """
+        Orphan path, not tied to a module spec or resource reader.
+        Can't be read and doesn't expose any meaningful children.
+        """
+
+        def __init__(self, *path_parts):
+            if len(path_parts) < 1:
+                raise ValueError('Need at least one path part to construct a path')
+            self._path = path_parts
+
+        def iterdir(self):
+            return iter(())
+
+        def is_file(self):
+            return False
+
+        is_dir = is_file
+
+        def joinpath(self, other):
+            return CompatibilityFiles.OrphanPath(*self._path, other)
+
+        @property
+        def name(self):
+            return self._path[-1]
+
+        def open(self, mode='r', *args, **kwargs):
+            raise FileNotFoundError("Can't open orphan path")
 
     def __init__(self, spec):
         self.spec = spec
@@ -71,7 +159,7 @@ class DegenerateFiles:
         return getattr(self._reader, attr)
 
     def files(self):
-        return DegenerateFiles.Path()
+        return CompatibilityFiles.SpecPath(self.spec, self._reader)
 
 
 def wrap_spec(package):
diff --git a/Lib/importlib/_common.py b/Lib/importlib/_common.py
index 549fee379a4..74654b34ed5 100644
--- a/Lib/importlib/_common.py
+++ b/Lib/importlib/_common.py
@@ -12,6 +12,7 @@ from .abc import ResourceReader, Traversable
 from ._adapters import wrap_spec
 
 Package = Union[types.ModuleType, str]
+Resource = Union[str, os.PathLike]
 
 
 def files(package):
@@ -93,7 +94,7 @@ def _tempfile(reader, suffix=''):
     finally:
         try:
             os.remove(raw_path)
-        except FileNotFoundError:
+        except (FileNotFoundError, PermissionError):
             pass
 
 
diff --git a/Lib/importlib/_itertools.py b/Lib/importlib/_itertools.py
new file mode 100644
index 00000000000..dd45f2f0966
--- /dev/null
+++ b/Lib/importlib/_itertools.py
@@ -0,0 +1,19 @@
+from itertools import filterfalse
+
+
+def unique_everseen(iterable, key=None):
+    "List unique elements, preserving order. Remember all elements ever seen."
+    # unique_everseen('AAAABBBCCDAABBB') --> A B C D
+    # unique_everseen('ABBCcAD', str.lower) --> A B C D
+    seen = set()
+    seen_add = seen.add
+    if key is None:
+        for element in filterfalse(seen.__contains__, iterable):
+            seen_add(element)
+            yield element
+    else:
+        for element in iterable:
+            k = key(element)
+            if k not in seen:
+                seen_add(k)
+                yield element
diff --git a/Lib/importlib/_legacy.py b/Lib/importlib/_legacy.py
new file mode 100644
index 00000000000..2ddec5f90a3
--- /dev/null
+++ b/Lib/importlib/_legacy.py
@@ -0,0 +1,84 @@
+import os
+import pathlib
+import types
+
+from typing import Union, Iterable, ContextManager, BinaryIO, TextIO
+
+from . import _common
+
+Package = Union[types.ModuleType, str]
+Resource = Union[str, os.PathLike]
+
+
+def open_binary(package: Package, resource: Resource) -> BinaryIO:
+    """Return a file-like object opened for binary reading of the resource."""
+    return (_common.files(package) / _common.normalize_path(resource)).open('rb')
+
+
+def read_binary(package: Package, resource: Resource) -> bytes:
+    """Return the binary contents of the resource."""
+    return (_common.files(package) / _common.normalize_path(resource)).read_bytes()
+
+
+def open_text(
+    package: Package,
+    resource: Resource,
+    encoding: str = 'utf-8',
+    errors: str = 'strict',
+) -> TextIO:
+    """Return a file-like object opened for text reading of the resource."""
+    return (_common.files(package) / _common.normalize_path(resource)).open(
+        'r', encoding=encoding, errors=errors
+    )
+
+
+def read_text(
+    package: Package,
+    resource: Resource,
+    encoding: str = 'utf-8',
+    errors: str = 'strict',
+) -> str:
+    """Return the decoded string of the resource.
+
+    The decoding-related arguments have the same semantics as those of
+    bytes.decode().
+    """
+    with open_text(package, resource, encoding, errors) as fp:
+        return fp.read()
+
+
+def contents(package: Package) -> Iterable[str]:
+    """Return an iterable of entries in `package`.
+
+    Note that not all entries are resources.  Specifically, directories are
+    not considered resources.  Use `is_resource()` on each entry returned here
+    to check if it is a resource or not.
+    """
+    return [path.name for path in _common.files(package).iterdir()]
+
+
+def is_resource(package: Package, name: str) -> bool:
+    """True if `name` is a resource inside `package`.
+
+    Directories are *not* resources.
+    """
+    resource = _common.normalize_path(name)
+    return any(
+        traversable.name == resource and traversable.is_file()
+        for traversable in _common.files(package).iterdir()
+    )
+
+
+def path(
+    package: Package,
+    resource: Resource,
+) -> ContextManager[pathlib.Path]:
+    """A context manager providing a file path object to the resource.
+
+    If the resource does not already exist on its own on the file system,
+    a temporary file will be created. If the file was created, the file
+    will be deleted upon exiting the context manager (no exception is
+    raised if the file was deleted prior to the context manager
+    exiting).
+    """
+    return _common.as_file(_common.files(package) / _common.normalize_path(resource))
diff --git a/Lib/importlib/readers.py b/Lib/importlib/readers.py
index 41089c071d8..b470a2062b2 100644
--- a/Lib/importlib/readers.py
+++ b/Lib/importlib/readers.py
@@ -1,8 +1,12 @@
 import collections
-import zipfile
+import operator
 import pathlib
+import zipfile
+
 from . import abc
 
+from ._itertools import unique_everseen
+
 
 def remove_duplicates(items):
     return iter(collections.OrderedDict.fromkeys(items))
@@ -63,13 +67,8 @@ class MultiplexedPath(abc.Traversable):
             raise NotADirectoryError('MultiplexedPath only supports directories')
 
     def iterdir(self):
-        visited = []
-        for path in self._paths:
-            for file in path.iterdir():
-                if file.name in visited:
-                    continue
-                visited.append(file.name)
-                yield file
+        files = (file for path in self._paths for file in path.iterdir())
+        return unique_everseen(files, key=operator.attrgetter('name'))
 
     def read_bytes(self):
         raise FileNotFoundError(f'{self} is not a file')
diff --git a/Lib/importlib/resources.py b/Lib/importlib/resources.py
index bb5c354d9f0..6cc46283ba0 100644
--- a/Lib/importlib/resources.py
+++ b/Lib/importlib/resources.py
@@ -1,19 +1,23 @@
-import os
-import io
+"""Read resources contained within a package."""
 
-from . import _common
-from ._common import as_file, files
-from .abc import ResourceReader
-from contextlib import suppress
-from importlib.abc import ResourceLoader
-from importlib.machinery import ModuleSpec
-from io import BytesIO, TextIOWrapper
-from pathlib import Path
-from types import ModuleType
-from typing import ContextManager, Iterable, Union
-from typing import cast, BinaryIO, TextIO
-from collections.abc import Sequence
-from functools import singledispatch
+from ._common import (
+    as_file,
+    files,
+    Package,
+    Resource,
+)
+
+from ._legacy import (
+    contents,
+    open_binary,
+    read_binary,
+    open_text,
+    read_text,
+    is_resource,
+    path,
+)
+
+from importlib.abc import ResourceReader
 
 
 __all__ = [
@@ -30,155 +34,3 @@ __all__ = [
     'read_binary',
     'read_text',
 ]
-
-
-Package = Union[str, ModuleType]
-Resource = Union[str, os.PathLike]
-
-
-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)
-    if reader is not None:
-        return reader.open_resource(resource)
-    spec = cast(ModuleSpec, package.__spec__)
-    # Using pathlib doesn't work well here due to the lack of 'strict'
-    # argument for pathlib.Path.resolve() prior to Python 3.6.
-    if spec.submodule_search_locations is not None:
-        paths = spec.submodule_search_locations
-    elif spec.origin is not None:
-        paths = [os.path.dirname(os.path.abspath(spec.origin))]
-
-    for package_path in paths:
-        full_path = os.path.join(package_path, resource)
-        try:
-            return open(full_path, mode='rb')
-        except OSError:
-            # Just assume the loader is a resource loader; all the relevant
-            # importlib.machinery loaders are and an AttributeError for
-            # get_data() will make it clear what is needed from the loader.
-            loader = cast(ResourceLoader, spec.loader)
-            data = None
-            if hasattr(spec.loader, 'get_data'):
-                with suppress(OSError):
-                    data = loader.get_data(full_path)
-            if data is not None:
-                return BytesIO(data)
-
-    raise FileNotFoundError(f'{resource!r} resource not found in {spec.name!r}')
-
-
-def open_text(
-    package: Package,
-    resource: Resource,
-    encoding: str = 'utf-8',
-    errors: str = 'strict',
-) -> TextIO:
-    """Return a file-like object opened for text reading of the resource."""
-    return TextIOWrapper(
-        open_binary(package, resource), encoding=encoding, errors=errors
-    )
-
-
-def read_binary(package: Package, resource: Resource) -> bytes:
-    """Return the binary contents of the resource."""
-    with open_binary(package, resource) as fp:
-        return fp.read()
-
-
-def read_text(
-    package: Package,
-    resource: Resource,
-    encoding: str = 'utf-8',
-    errors: str = 'strict',
-) -> str:
-    """Return the decoded string of the resource.
-
-    The decoding-related arguments have the same semantics as those of
-    bytes.decode().
-    """
-    with open_text(package, resource, encoding, errors) as fp:
-        return fp.read()
-
-
-def path(
-    package: Package,
-    resource: Resource,
-) -> 'ContextManager[Path]':
-    """A context manager providing a file path object to the resource.
-
-    If the resource does not already exist on its own on the file system,
-    a temporary file will be created. If the file was created, the file
-    will be deleted upon exiting the context manager (no exception is
-    raised if the file was deleted prior to the context manager
-    exiting).
-    """
-    reader = _common.get_resource_reader(_common.get_package(package))
-    return (
-        _path_from_reader(reader, _common.normalize_path(resource))
-        if reader
-        else _common.as_file(
-            _common.files(package).joinpath(_common.normalize_path(resource))
-        )
-    )
-
-
-def _path_from_reader(reader, resource):
-    return _path_from_resource_path(reader, resource) or _path_from_open_resource(
-        reader, resource
-    )
-
-
-def _path_from_resource_path(reader, resource):
-    with suppress(FileNotFoundError):
-        return Path(reader.resource_path(resource))
-
-
-def _path_from_open_resource(reader, resource):
-    saved = io.BytesIO(reader.open_resource(resource).read())
-    return _common._tempfile(saved.read, suffix=resource)
-
-
-def is_resource(package: Package, name: str) -> bool:
-    """True if 'name' is a resource inside 'package'.
-
-    Directories are *not* resources.
-    """
-    package = _common.get_package(package)
-    _common.normalize_path(name)
-    reader = _common.get_resource_reader(package)
-    if reader is not None:
-        return reader.is_resource(name)
-    package_contents = set(contents(package))
-    if name not in package_contents:
-        return False
-    return (_common.from_package(package) / name).is_file()
-
-
-def contents(package: Package) -> Iterable[str]:
-    """Return an iterable of entries in 'package'.
-
-    Note that not all entries are resources.  Specifically, directories are
-    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)
-    if reader is not None:
-        return _ensure_sequence(reader.contents())
-    transversable = _common.from_package(package)
-    if transversable.is_dir():
-        return list(item.name for item in transversable.iterdir())
-    return []
-
-
-@singledispatch
-def _ensure_sequence(iterable):
-    return list(iterable)
-
-
-@_ensure_sequence.register(Sequence)
-def _(iterable):
-    return iterable
diff --git a/Lib/importlib/simple.py b/Lib/importlib/simple.py
new file mode 100644
index 00000000000..da073cbdb11
--- /dev/null
+++ b/Lib/importlib/simple.py
@@ -0,0 +1,116 @@
+"""
+Interface adapters for low-level readers.
+"""
+
+import abc
+import io
+import itertools
+from typing import BinaryIO, List
+
+from .abc import Traversable, TraversableResources
+
+
+class SimpleReader(abc.ABC):
+    """
+    The minimum, low-level interface required from a resource
+    provider.
+    """
+
+    @abc.abstractproperty
+    def package(self):
+        # type: () -> str
+        """
+        The name of the package for which this reader loads resources.
+        """
+
+    @abc.abstractmethod
+    def children(self):
+        # type: () -> List['SimpleReader']
+        """
+        Obtain an iterable of SimpleReader for available
+        child containers (e.g. directories).
+        """
+
+    @abc.abstractmethod
+    def resources(self):
+        # type: () -> List[str]
+        """
+        Obtain available named resources for this virtual package.
+        """
+
+    @abc.abstractmethod
+    def open_binary(self, resource):
+        # type: (str) -> BinaryIO
+        """
+        Obtain a File-like for a named resource.
+        """
+
+    @property
+    def name(self):
+        return self.package.split('.')[-1]
+
+
+class ResourceHandle(Traversable):
+    """
+    Handle to a named resource in a ResourceReader.
+    """
+
+    def __init__(self, parent, name):
+        # type: (ResourceContainer, str) -> None
+        self.parent = parent
+        self.name = name  # type: ignore
+
+    def is_file(self):
+        return True
+
+    def is_dir(self):
+        return False
+
+    def open(self, mode='r', *args, **kwargs):
+        stream = self.parent.reader.open_binary(self.name)
+        if 'b' not in mode:
+            stream = io.TextIOWrapper(*args, **kwargs)
+        return stream
+
+    def joinpath(self, name):
+        raise RuntimeError("Cannot traverse into a resource")
+
+
+class ResourceContainer(Traversable):
+    """
+    Traversable container for a package's resources via its reader.
+    """
+
+    def __init__(self, reader):
+        # type: (SimpleReader) -> None
+        self.reader = reader
+
+    def is_dir(self):
+        return True
+
+    def is_file(self):
+        return False
+
+    def iterdir(self):
+        files = (ResourceHandle(self, name) for name in self.reader.resources)
+        dirs = map(ResourceContainer, self.reader.children())
+        return itertools.chain(files, dirs)
+
+    def open(self, *args, **kwargs):
+        raise IsADirectoryError()
+
+    def joinpath(self, name):
+        return next(
+            traversable for traversable in self.iterdir() if traversable.name == name
+        )
+
+
+class TraversableReader(TraversableResources, SimpleReader):
+    """
+    A TraversableResources based on SimpleReader. Resource providers
+    may derive from this class to provide the TraversableResources
+    interface by supplying the SimpleReader interface.
+    """
+
+    def files(self):
+        return ResourceContainer(self)
diff --git a/Lib/test/test_importlib/resources/__init__.py b/Lib/test/test_importlib/resources/__init__.py
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/Lib/test/test_importlib/resources/util.py b/Lib/test/test_importlib/resources/util.py
new file mode 100644
index 00000000000..d7a049bf804
--- /dev/null
+++ b/Lib/test/test_importlib/resources/util.py
@@ -0,0 +1,190 @@
+import abc
+import importlib
+import io
+import sys
+import types
+from pathlib import Path, PurePath
+
+from .. import data01
+from .. import zipdata01
+from importlib.abc import ResourceReader
+from test.support import import_helper
+
+
+from importlib.machinery import ModuleSpec
+
+
+class Reader(ResourceReader):
+    def __init__(self, **kwargs):
+        vars(self).update(kwargs)
+
+    def get_resource_reader(self, package):
+        return self
+
+    def open_resource(self, path):
+        self._path = path
+        if isinstance(self.file, Exception):
+            raise self.file
+        return self.file
+
+    def resource_path(self, path_):
+        self._path = path_
+        if isinstance(self.path, Exception):
+            raise self.path
+        return self.path
+
+    def is_resource(self, path_):
+        self._path = path_
+        if isinstance(self.path, Exception):
+            raise self.path
+
+        def part(entry):
+            return entry.split('/')
+
+        return any(
+            len(parts) == 1 and parts[0] == path_ for parts in map(part, self._contents)
+        )
+
+    def contents(self):
+        if isinstance(self.path, Exception):
+            raise self.path
+        yield from self._contents
+
+
+def create_package_from_loader(loader, is_package=True):
+    name = 'testingpackage'
+    module = types.ModuleType(name)
+    spec = ModuleSpec(name, loader, origin='does-not-exist', is_package=is_package)
+    module.__spec__ = spec
+    module.__loader__ = loader
+    return module
+
+
+def create_package(file=None, path=None, is_package=True, contents=()):
+    return create_package_from_loader(
+        Reader(file=file, path=path, _contents=contents),
+        is_package,
+    )
+
+
+class CommonTests(metaclass=abc.ABCMeta):
+    """
+    Tests shared by test_open, test_path, and test_read.
+    """
+
+    @abc.abstractmethod
+    def execute(self, package, path):
+        """
+        Call the pertinent legacy API function (e.g. open_text, path)
+        on package and path.
+        """
+
+    def test_package_name(self):
+        # Passing in the package name should succeed.
+        self.execute(data01.__name__, 'utf-8.file')
+
+    def test_package_object(self):
+        # Passing in the package itself should succeed.
+        self.execute(data01, 'utf-8.file')
+
+    def test_string_path(self):
+        # Passing in a string for the path should succeed.
+        path = 'utf-8.file'
+        self.execute(data01, path)
+
+    def test_pathlib_path(self):
+        # Passing in a pathlib.PurePath object for the path should succeed.
+        path = PurePath('utf-8.file')
+        self.execute(data01, path)
+
+    def test_absolute_path(self):
+        # An absolute path is a ValueError.
+        path = Path(__file__)
+        full_path = path.parent / 'utf-8.file'
+        with self.assertRaises(ValueError):
+            self.execute(data01, full_path)
+
+    def test_relative_path(self):
+        # A reative path is a ValueError.
+        with self.assertRaises(ValueError):
+            self.execute(data01, '../data01/utf-8.file')
+
+    def test_importing_module_as_side_effect(self):
+        # The anchor package can already be imported.
+        del sys.modules[data01.__name__]
+        self.execute(data01.__name__, 'utf-8.file')
+
+    def test_non_package_by_name(self):
+        # The anchor package cannot be a module.
+        with self.assertRaises(TypeError):
+            self.execute(__name__, 'utf-8.file')
+
+    def test_non_package_by_package(self):
+        # The anchor package cannot be a module.
+        with self.assertRaises(TypeError):
+            module = sys.modules['test.test_importlib.resources.util']
+            self.execute(module, 'utf-8.file')
+
+    def test_missing_path(self):
+        # Attempting to open or read or request the path for a
+        # non-existent path should succeed if open_resource
+        # can return a viable data stream.
+        bytes_data = io.BytesIO(b'Hello, world!')
+        package = create_package(file=bytes_data, path=FileNotFoundError())
+        self.execute(package, 'utf-8.file')
+        self.assertEqual(package.__loader__._path, 'utf-8.file')
+
+    def test_extant_path(self):
+        # Attempting to open or read or request the path when the
+        # path does exist should still succeed. Does not assert
+        # anything about the result.
+        bytes_data = io.BytesIO(b'Hello, world!')
+        # any path that exists
+        path = __file__
+        package = create_package(file=bytes_data, path=path)
+        self.execute(package, 'utf-8.file')
+        self.assertEqual(package.__loader__._path, 'utf-8.file')
+
+    def test_useless_loader(self):
+        package = create_package(file=FileNotFoundError(), path=FileNotFoundError())
+        with self.assertRaises(FileNotFoundError):
+            self.execute(package, 'utf-8.file')
+
+
+class ZipSetupBase:
+    ZIP_MODULE = None
+
+    @classmethod
+    def setUpClass(cls):
+        data_path = Path(cls.ZIP_MODULE.__file__)
+        data_dir = data_path.parent
+        cls._zip_path = str(data_dir / 'ziptestdata.zip')
+        sys.path.append(cls._zip_path)
+        cls.data = importlib.import_module('ziptestdata')
+
+    @classmethod
+    def tearDownClass(cls):
+        try:
+            sys.path.remove(cls._zip_path)
+        except ValueError:
+            pass
+
+        try:
+            del sys.path_importer_cache[cls._zip_path]
+            del sys.modules[cls.data.__name__]
+        except KeyError:
+            pass
+
+        try:
+            del cls.data
+            del cls._zip_path
+        except AttributeError:
+            pass
+
+    def setUp(self):
+        modules = import_helper.modules_setup()
+        self.addCleanup(import_helper.modules_cleanup, *modules)
+
+
+class ZipSetup(ZipSetupBase):
+    ZIP_MODULE = zipdata01  # type: ignore
diff --git a/Lib/test/test_importlib/test_compatibilty_files.py b/Lib/test/test_importlib/test_compatibilty_files.py
new file mode 100644
index 00000000000..d703c060c44
--- /dev/null
+++ b/Lib/test/test_importlib/test_compatibilty_files.py
@@ -0,0 +1,102 @@
+import io
+import unittest
+
+from importlib import resources
+
+from importlib._adapters import (
+    CompatibilityFiles,
+    wrap_spec,
+)
+
+from .resources import util
+
+
+class CompatibilityFilesTests(unittest.TestCase):
+    @property
+    def package(self):
+        bytes_data = io.BytesIO(b'Hello, world!')
+        return util.create_package(
+            file=bytes_data,
+            path='some_path',
+            contents=('a', 'b', 'c'),
+        )
+
+    @property
+    def files(self):
+        return resources.files(self.package)
+
+    def test_spec_path_iter(self):
+        self.assertEqual(
+            sorted(path.name for path in self.files.iterdir()),
+            ['a', 'b', 'c'],
+        )
+
+    def test_child_path_iter(self):
+        self.assertEqual(list((self.files / 'a').iterdir()), [])
+
+    def test_orphan_path_iter(self):
+        self.assertEqual(list((self.files / 'a' / 'a').iterdir()), [])
+        self.assertEqual(list((self.files / 'a' / 'a' / 'a').iterdir()), [])
+
+    def test_spec_path_is(self):
+        self.assertFalse(self.files.is_file())
+        self.assertFalse(self.files.is_dir())
+
+    def test_child_path_is(self):
+        self.assertTrue((self.files / 'a').is_file())
+        self.assertFalse((self.files / 'a').is_dir())
+
+    def test_orphan_path_is(self):
+        self.assertFalse((self.files / 'a' / 'a').is_file())
+        self.assertFalse((self.files / 'a' / 'a').is_dir())
+        self.assertFalse((self.files / 'a' / 'a' / 'a').is_file())
+        self.assertFalse((self.files / 'a' / 'a' / 'a').is_dir())
+
+    def test_spec_path_name(self):
+        self.assertEqual(self.files.name, 'testingpackage')
+
+    def test_child_path_name(self):
+        self.assertEqual((self.files / 'a').name, 'a')
+
+    def test_orphan_path_name(self):
+        self.assertEqual((self.files / 'a' / 'b').name, 'b')
+        self.assertEqual((self.files / 'a' / 'b' / 'c').name, 'c')
+
+    def test_spec_path_open(self):
+        self.assertEqual(self.files.read_bytes(), b'Hello, world!')
+        self.assertEqual(self.files.read_text(), 'Hello, world!')
+
+    def test_child_path_open(self):
+        self.assertEqual((self.files / 'a').read_bytes(), b'Hello, world!')
+        self.assertEqual((self.files / 'a').read_text(), 'Hello, world!')
+
+    def test_orphan_path_open(self):
+        with self.assertRaises(FileNotFoundError):
+            (self.files / 'a' / 'b').read_bytes()
+        with self.assertRaises(FileNotFoundError):
+            (self.files / 'a' / 'b' / 'c').read_bytes()
+
+    def test_open_invalid_mode(self):
+        with self.assertRaises(ValueError):
+            self.files.open('0')
+
+    def test_orphan_path_invalid(self):
+        with self.assertRaises(ValueError):
+            CompatibilityFiles.OrphanPath()
+
+    def test_wrap_spec(self):
+        spec = wrap_spec(self.package)
+        self.assertIsInstance(spec.loader.get_resource_reader(None), CompatibilityFiles)
+
+
+class CompatibilityFilesNoReaderTests(unittest.TestCase):
+    @property
+    def package(self):
+        return util.create_package_from_loader(None)
+
+    @property
+    def files(self):
+        return resources.files(self.package)
+
+    def test_spec_path_joinpath(self):
+        self.assertIsInstance(self.files / 'a', CompatibilityFiles.OrphanPath)
diff --git a/Lib/test/test_importlib/test_contents.py b/Lib/test/test_importlib/test_contents.py
new file mode 100644
index 00000000000..0f3aa84f5b5
--- /dev/null
+++ b/Lib/test/test_importlib/test_contents.py
@@ -0,0 +1,42 @@
+import unittest
+from importlib import resources
+
+from . import data01
+from .resources import util
+
+
+class ContentsTests:
+    expected = {
+        '__init__.py',
+        'binary.file',
+        'subdirectory',
+        'utf-16.file',
+        'utf-8.file',
+    }
+
+    def test_contents(self):
+        assert self.expected <= set(resources.contents(self.data))
+
+
+class ContentsDiskTests(ContentsTests, unittest.TestCase):
+    def setUp(self):
+        self.data = data01
+
+
+class ContentsZipTests(ContentsTests, util.ZipSetup, unittest.TestCase):
+    pass
+
+
+class ContentsNamespaceTests(ContentsTests, unittest.TestCase):
+    expected = {
+        # no __init__ because of namespace design
+        # no subdirectory as incidental difference in fixture
+        'binary.file',
+        'utf-16.file',
+        'utf-8.file',
+    }
+
+    def setUp(self):
+        from . import namespacedata01
+
+        self.data = namespacedata01
diff --git a/Lib/test/test_importlib/test_files.py b/Lib/test/test_importlib/test_files.py
index 481829b7422..b9170d83bea 100644
--- a/Lib/test/test_importlib/test_files.py
+++ b/Lib/test/test_importlib/test_files.py
@@ -4,7 +4,7 @@ import unittest
 from importlib import resources
 from importlib.abc import Traversable
 from . import data01
-from . import util
+from .resources import util
 
 
 class FilesTests:
@@ -35,5 +35,12 @@ class OpenZipTests(FilesTests, util.ZipSetup, unittest.TestCase):
     pass
 
 
+class OpenNamespaceTests(FilesTests, unittest.TestCase):
+    def setUp(self):
+        from . import namespacedata01
+
+        self.data = namespacedata01
+
+
 if __name__ == '__main__':
     unittest.main()
diff --git a/Lib/test/test_importlib/test_open.py b/Lib/test/test_importlib/test_open.py
index b75675f43b6..6f88ff78b73 100644
--- a/Lib/test/test_importlib/test_open.py
+++ b/Lib/test/test_importlib/test_open.py
@@ -2,16 +2,16 @@ import unittest
 
 from importlib import resources
 from . import data01
-from . import util
+from .resources import util
 
 
-class CommonBinaryTests(util.CommonResourceTests, unittest.TestCase):
+class CommonBinaryTests(util.CommonTests, unittest.TestCase):
     def execute(self, package, path):
         with resources.open_binary(package, path):
             pass
 
 
-class CommonTextTests(util.CommonResourceTests, unittest.TestCase):
+class CommonTextTests(util.CommonTests, unittest.TestCase):
     def execute(self, package, path):
         with resources.open_text(package, path):
             pass
diff --git a/Lib/test/test_importlib/test_path.py b/Lib/test/test_importlib/test_path.py
index d6ed09a9e0d..4436d7f34ef 100644
--- a/Lib/test/test_importlib/test_path.py
+++ b/Lib/test/test_importlib/test_path.py
@@ -3,10 +3,10 @@ import unittest
 
 from importlib import resources
 from . import data01
-from . import util
+from .resources import util
 
 
-class CommonTests(util.CommonResourceTests, unittest.TestCase):
+class CommonTests(util.CommonTests, unittest.TestCase):
     def execute(self, package, path):
         with resources.path(package, path):
             pass
diff --git a/Lib/test/test_importlib/test_read.py b/Lib/test/test_importlib/test_read.py
index f6ec13af62d..357980132b6 100644
--- a/Lib/test/test_importlib/test_read.py
+++ b/Lib/test/test_importlib/test_read.py
@@ -2,15 +2,15 @@ import unittest
 
 from importlib import import_module, resources
 from . import data01
-from . import util
+from .resources import util
 
 
-class CommonBinaryTests(util.CommonResourceTests, unittest.TestCase):
+class CommonBinaryTests(util.CommonTests, unittest.TestCase):
     def execute(self, package, path):
         resources.read_binary(package, path)
 
 
-class CommonTextTests(util.CommonResourceTests, unittest.TestCase):
+class CommonTextTests(util.CommonTests, unittest.TestCase):
     def execute(self, package, path):
         resources.read_text(package, path)
 
@@ -55,5 +55,12 @@ class ReadZipTests(ReadTests, util.ZipSetup, unittest.TestCase):
         self.assertEqual(result, b'\0\1\2\3')
 
 
+class ReadNamespaceTests(ReadTests, unittest.TestCase):
+    def setUp(self):
+        from . import namespacedata01
+
+        self.data = namespacedata01
+
+
 if __name__ == '__main__':
     unittest.main()
diff --git a/Lib/test/test_importlib/test_resource.py b/Lib/test/test_importlib/test_resource.py
index 003f7e95ad9..612bada5e03 100644
--- a/Lib/test/test_importlib/test_resource.py
+++ b/Lib/test/test_importlib/test_resource.py
@@ -5,7 +5,7 @@ import pathlib
 
 from . import data01
 from . import zipdata01, zipdata02
-from . import util
+from .resources import util
 from importlib import resources, import_module
 from test.support import import_helper
 from test.support.os_helper import unlink
@@ -33,14 +33,14 @@ class ResourceTests:
         # are not germane to this test, so just filter them out.
         contents.discard('__pycache__')
         self.assertEqual(
-            contents,
-            {
+            sorted(contents),
+            [
                 '__init__.py',
-                'subdirectory',
-                'utf-8.file',
                 'binary.file',
+                'subdirectory',
                 'utf-16.file',
-            },
+                'utf-8.file',
+            ],
         )
 
 
diff --git a/Lib/test/test_importlib/util.py b/Lib/test/test_importlib/util.py
index ca0d8c9b6eb..c07ac2a64c2 100644
--- a/Lib/test/test_importlib/util.py
+++ b/Lib/test/test_importlib/util.py
@@ -1,17 +1,11 @@
-import abc
 import builtins
 import contextlib
 import errno
 import functools
-import importlib
 from importlib import machinery, util, invalidate_caches
-from importlib.abc import ResourceReader
-import io
 import marshal
 import os
 import os.path
-from pathlib import Path, PurePath
-from test import support
 from test.support import import_helper
 from test.support import os_helper
 import unittest
@@ -19,9 +13,6 @@ import sys
 import tempfile
 import types
 
-from . import data01
-from . import zipdata01
-
 
 BUILTINS = types.SimpleNamespace()
 BUILTINS.good_name = None
@@ -417,166 +408,3 @@ class CASEOKTestBase:
         if any(x in self.importlib._bootstrap_external._os.environ
                     for x in possibilities) != should_exist:
             self.skipTest('os.environ changes not reflected in _os.environ')
-
-
-def create_package(file, path, is_package=True, contents=()):
-    class Reader(ResourceReader):
-        def get_resource_reader(self, package):
-            return self
-
-        def open_resource(self, path):
-            self._path = path
-            if isinstance(file, Exception):
-                raise file
-            else:
-                return file
-
-        def resource_path(self, path_):
-            self._path = path_
-            if isinstance(path, Exception):
-                raise path
-            else:
-                return path
-
-        def is_resource(self, path_):
-            self._path = path_
-            if isinstance(path, Exception):
-                raise path
-            for entry in contents:
-                parts = entry.split('/')
-                if len(parts) == 1 and parts[0] == path_:
-                    return True
-            return False
-
-        def contents(self):
-            if isinstance(path, Exception):
-                raise path
-            # There's no yield from in baseball, er, Python 2.
-            for entry in contents:
-                yield entry
-
-    name = 'testingpackage'
-    # Unfortunately importlib.util.module_from_spec() was not introduced until
-    # Python 3.5.
-    module = types.ModuleType(name)
-    loader = Reader()
-    spec = machinery.ModuleSpec(
-        name, loader,
-        origin='does-not-exist',
-        is_package=is_package)
-    module.__spec__ = spec
-    module.__loader__ = loader
-    return module
-
-
-class CommonResourceTests(abc.ABC):
-    @abc.abstractmethod
-    def execute(self, package, path):
-        raise NotImplementedError
-
-    def test_package_name(self):
-        # Passing in the package name should succeed.
-        self.execute(data01.__name__, 'utf-8.file')
-
-    def test_package_object(self):
-        # Passing in the package itself should succeed.
-        self.execute(data01, 'utf-8.file')
-
-    def test_string_path(self):
-        # Passing in a string for the path should succeed.
-        path = 'utf-8.file'
-        self.execute(data01, path)
-
-    @unittest.skipIf(sys.version_info < (3, 6), 'requires os.PathLike support')
-    def test_pathlib_path(self):
-        # Passing in a pathlib.PurePath object for the path should succeed.
-        path = PurePath('utf-8.file')
-        self.execute(data01, path)
-
-    def test_absolute_path(self):
-        # An absolute path is a ValueError.
-        path = Path(__file__)
-        full_path = path.parent/'utf-8.file'
-        with self.assertRaises(ValueError):
-            self.execute(data01, full_path)
-
-    def test_relative_path(self):
-        # A relative path is a ValueError.
-        with self.assertRaises(ValueError):
-            self.execute(data01, '../data01/utf-8.file')
-
-    def test_importing_module_as_side_effect(self):
-        # The anchor package can already be imported.
-        del sys.modules[data01.__name__]
-        self.execute(data01.__name__, 'utf-8.file')
-
-    def test_non_package_by_name(self):
-        # The anchor package cannot be a module.
-        with self.assertRaises(TypeError):
-            self.execute(__name__, 'utf-8.file')
-
-    def test_non_package_by_package(self):
-        # The anchor package cannot be a module.
-        with self.assertRaises(TypeError):
-            module = sys.modules['test.test_importlib.util']
-            self.execute(module, 'utf-8.file')
-
-    @unittest.skipIf(sys.version_info < (3,), 'No ResourceReader in Python 2')
-    def test_resource_opener(self):
-        bytes_data = io.BytesIO(b'Hello, world!')
-        package = create_package(file=bytes_data, path=FileNotFoundError())
-        self.execute(package, 'utf-8.file')
-        self.assertEqual(package.__loader__._path, 'utf-8.file')
-
-    @unittest.skipIf(sys.version_info < (3,), 'No ResourceReader in Python 2')
-    def test_resource_path(self):
-        bytes_data = io.BytesIO(b'Hello, world!')
-        path = __file__
-        package = create_package(file=bytes_data, path=path)
-        self.execute(package, 'utf-8.file')
-        self.assertEqual(package.__loader__._path, 'utf-8.file')
-
-    def test_useless_loader(self):
-        package = create_package(file=FileNotFoundError(),
-                                 path=FileNotFoundError())
-        with self.assertRaises(FileNotFoundError):
-            self.execute(package, 'utf-8.file')
-
-
-class ZipSetupBase:
-    ZIP_MODULE = None
-
-    @classmethod
-    def setUpClass(cls):
-        data_path = Path(cls.ZIP_MODULE.__file__)
-        data_dir = data_path.parent
-        cls._zip_path = str(data_dir / 'ziptestdata.zip')
-        sys.path.append(cls._zip_path)
-        cls.data = importlib.import_module('ziptestdata')
-
-    @classmethod
-    def tearDownClass(cls):
-        try:
-            sys.path.remove(cls._zip_path)
-        except ValueError:
-            pass
-
-        try:
-            del sys.path_importer_cache[cls._zip_path]
-            del sys.modules[cls.data.__name__]
-        except KeyError:
-            pass
-
-        try:
-            del cls.data
-            del cls._zip_path
-        except AttributeError:
-            pass
-
-    def setUp(self):
-        modules = import_helper.modules_setup()
-        self.addCleanup(import_helper.modules_cleanup, *modules)
-
-
-class ZipSetup(ZipSetupBase):
-    ZIP_MODULE = zipdata01                          # type: ignore
diff --git a/Misc/NEWS.d/next/Library/2021-07-28-22-53-18.bpo-44771.BvLdnU.rst b/Misc/NEWS.d/next/Library/2021-07-28-22-53-18.bpo-44771.BvLdnU.rst
new file mode 100644
index 00000000000..0d47a55a7d7
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-07-28-22-53-18.bpo-44771.BvLdnU.rst
@@ -0,0 +1,5 @@
+Added ``importlib.simple`` module implementing adapters from a low-level
+resources reader interface to a ``TraversableResources`` interface. Legacy
+API (``path``, ``contents``, ...) is now supported entirely by the
+``.files()`` API with a compatibility shim supplied for resource loaders
+without that functionality. Feature parity with ``importlib_resources`` 5.2.