bpo-41490: `path and contents` to aggressively close handles (#22915)

* bpo-41490: ``path`` method to aggressively close handles

* Add blurb

* In ZipReader.contents, eagerly evaluate the contents to release references to the zipfile.

* Instead use _ensure_sequence to ensure any iterable from a reader is eagerly converted to a list if it's not already a sequence.

Lib/test/test_importlib/test_resource.py

@@ -1,10 +1,14 @@
 import sys
 import unittest
+import uuid
+import pathlib
 
 from . import data01
 from . import zipdata01, zipdata02
 from . import util
 from importlib import resources, import_module
+from test.support import import_helper
+from test.support.os_helper import unlink
 
 
 class ResourceTests:
@@ -162,5 +166,80 @@ def test_namespaces_cannot_have_resources(self):
             'test.test_importlib.data03.namespace', 'resource1.txt')
 
 
+class DeletingZipsTest(unittest.TestCase):
+    """Having accessed resources in a zip file should not keep an open
+    reference to the zip.
+    """
+    ZIP_MODULE = zipdata01
+
+    def setUp(self):
+        modules = import_helper.modules_setup()
+        self.addCleanup(import_helper.modules_cleanup, *modules)
+
+        data_path = pathlib.Path(self.ZIP_MODULE.__file__)
+        data_dir = data_path.parent
+        self.source_zip_path = data_dir / 'ziptestdata.zip'
+        self.zip_path = pathlib.Path('{}.zip'.format(uuid.uuid4())).absolute()
+        self.zip_path.write_bytes(self.source_zip_path.read_bytes())
+        sys.path.append(str(self.zip_path))
+        self.data = import_module('ziptestdata')
+
+    def tearDown(self):
+        try:
+            sys.path.remove(str(self.zip_path))
+        except ValueError:
+            pass
+
+        try:
+            del sys.path_importer_cache[str(self.zip_path)]
+            del sys.modules[self.data.__name__]
+        except KeyError:
+            pass
+
+        try:
+            unlink(self.zip_path)
+        except OSError:
+            # If the test fails, this will probably fail too
+            pass
+
+    def test_contents_does_not_keep_open(self):
+        c = resources.contents('ziptestdata')
+        self.zip_path.unlink()
+        del c
+
+    def test_is_resource_does_not_keep_open(self):
+        c = resources.is_resource('ziptestdata', 'binary.file')
+        self.zip_path.unlink()
+        del c
+
+    def test_is_resource_failure_does_not_keep_open(self):
+        c = resources.is_resource('ziptestdata', 'not-present')
+        self.zip_path.unlink()
+        del c
+
+    @unittest.skip("Desired but not supported.")
+    def test_path_does_not_keep_open(self):
+        c = resources.path('ziptestdata', 'binary.file')
+        self.zip_path.unlink()
+        del c
+
+    def test_entered_path_does_not_keep_open(self):
+        # This is what certifi does on import to make its bundle
+        # available for the process duration.
+        c = resources.path('ziptestdata', 'binary.file').__enter__()
+        self.zip_path.unlink()
+        del c
+
+    def test_read_binary_does_not_keep_open(self):
+        c = resources.read_binary('ziptestdata', 'binary.file')
+        self.zip_path.unlink()
+        del c
+
+    def test_read_text_does_not_keep_open(self):
+        c = resources.read_text('ziptestdata', 'utf-8.file', encoding='utf-8')
+        self.zip_path.unlink()
+        del c
+
+
 if __name__ == '__main__':
     unittest.main()