merge

Doc/library/importlib.rst

@@ -722,6 +722,10 @@ find and load modules.
      Calls :meth:`importlib.abc.PathEntryFinder.invalidate_caches` on all
      finders stored in :attr:`sys.path_importer_cache`.
 
+  .. versionchanged:: 3.4
+     Calls objects in :data:sys.path_hooks with the current working directory
+     for ``''`` (i.e. the empty string).
+
 
 .. class:: FileFinder(path, \*loader_details)
 
@@ -748,6 +752,9 @@ find and load modules.
 
    .. versionadded:: 3.3
 
+   .. versionchange:: 3.4
+      The empty string is no longer special-cased to be changed into ``'.'``.
+
    .. attribute:: path
 
       The path the finder will search in.

Doc/whatsnew/3.4.rst

@@ -675,3 +675,14 @@ that may require changes to your code.
   :c:func:`PyMem_RawRealloc`, or *NULL* if an error occurred, instead of a
   string allocated by :c:func:`PyMem_Malloc` or :c:func:`PyMem_Realloc`.
 
+* :cls:`importlib.machinery.PathFinder` now passes on the current working
+  directory to objects in :data:`sys.path_hooks` for the empty string. This
+  results in :data:`sys.path_importer_cache` never containing ``''``, thus
+  iterating through :data:`sys.path_importer_cache` based on :data:`sys.path`
+  will not find all keys. A module's ``__file__`` when imported in the current
+  working directory will also now have an absolute path, including when using
+  ``-m`` with the interpreter (this does not influence when the path to a file
+  is specified on the command-line).
+
+* :cls:`importlib.machinery.FileFinder` no longer special-cases the empty string
+  to be changed to ``'.'``.

Lib/importlib/_bootstrap.py

@@ -1302,7 +1302,7 @@ class PathFinder:
 
         """
         if path == '':
-            path = '.'
+            path = _os.getcwd()
         try:
             finder = sys.path_importer_cache[path]
         except KeyError:
@@ -1373,7 +1373,7 @@ class FileFinder:
             loaders.extend((suffix, loader) for suffix in suffixes)
         self._loaders = loaders
         # Base (directory) path
-        self.path = path or '.'
+        self.path = path
         self._path_mtime = -1
         self._path_cache = set()
         self._relaxed_path_cache = set()

Lib/test/test_importlib/import_/test_path.py

@@ -82,11 +82,11 @@ class FinderTests(unittest.TestCase):
         path = ''
         module = '<test module>'
         importer = util.mock_modules(module)
-        hook = import_util.mock_path_hook(os.curdir, importer=importer)
+        hook = import_util.mock_path_hook(os.getcwd(), importer=importer)
         with util.import_state(path=[path], path_hooks=[hook]):
             loader = machinery.PathFinder.find_module(module)
             self.assertIs(loader, importer)
-            self.assertIn(os.curdir, sys.path_importer_cache)
+            self.assertIn(os.getcwd(), sys.path_importer_cache)
 
     def test_None_on_sys_path(self):
         # Putting None in sys.path[0] caused an import regression from Python

Misc/NEWS

@@ -10,6 +10,13 @@ Projected release date: 2013-10-20
 Core and Builtins
 -----------------
 
+- Issue #18416: importlib.machinery.PathFinder now treats '' as the cwd and
+  importlib.machinery.FileFinder no longer special-cases '' to '.'. This leads
+  to modules imported from cwd to now possess an absolute file path for
+  __file__ (this does not affect modules specified by path on the CLI but it
+  does affect -m/runpy). It also allows FileFinder to be more consistent by not
+  having an edge case.
+
 - Issue #4555: All exported C symbols are now prefixed with either
   "Py" or "_Py".