gh-91181: drop support for bytes on sys.path (GH-31934)

Support for bytes broke sometime between Python 3.2 and 3.6 and has been broken ever since. Trying to bring back supports is surprisingly difficult in the face of -b and checking for keys in sys.path_importer_cache. Since the support was broken for so long, trying to overcome the difficulty of bringing back the support has been deemed not worth it.

Co-authored-by: Eryk Sun <eryksun@gmail.com>
Co-authored-by: Brett Cannon <brett@python.org>

Doc/library/sys.rst

@@ -1158,7 +1158,7 @@ always available.
    line option or the :envvar:`PYTHONSAFEPATH` environment variable?
 
    A program is free to modify this list for its own purposes.  Only strings
-   and bytes should be added to :data:`sys.path`; all other data types are
+   should be added to :data:`sys.path`; all other data types are
    ignored during import.
 
 

Doc/reference/import.rst

@@ -800,10 +800,8 @@ environment variable and various other installation- and
 implementation-specific defaults.  Entries in :data:`sys.path` can name
 directories on the file system, zip files, and potentially other "locations"
 (see the :mod:`site` module) that should be searched for modules, such as
-URLs, or database queries.  Only strings and bytes should be present on
-:data:`sys.path`; all other data types are ignored.  The encoding of bytes
-entries is determined by the individual :term:`path entry finders <path entry
-finder>`.
+URLs, or database queries.  Only strings should be present on
+:data:`sys.path`; all other data types are ignored.
 
 The :term:`path based finder` is a :term:`meta path finder`, so the import
 machinery begins the :term:`import path` search by calling the path

Lib/importlib/_bootstrap_external.py

@@ -1475,7 +1475,7 @@ def _get_spec(cls, fullname, path, target=None):
         #  the list of paths that will become its __path__
         namespace_path = []
         for entry in path:
-            if not isinstance(entry, (str, bytes)):
+            if not isinstance(entry, str):
                 continue
             finder = cls._path_importer_cache(entry)
             if finder is not None:

Lib/test/test_zipimport.py

@@ -742,7 +742,8 @@ def testBytesPath(self):
             z.writestr(zinfo, test_src)
 
         zipimport.zipimporter(filename)
-        zipimport.zipimporter(os.fsencode(filename))
+        with self.assertRaises(TypeError):
+            zipimport.zipimporter(os.fsencode(filename))
         with self.assertRaises(TypeError):
             zipimport.zipimporter(bytearray(os.fsencode(filename)))
         with self.assertRaises(TypeError):

Lib/zipimport.py

@@ -63,8 +63,7 @@ class zipimporter(_bootstrap_external._LoaderBasics):
     # if found, or else read it from the archive.
     def __init__(self, path):
         if not isinstance(path, str):
-            import os
-            path = os.fsdecode(path)
+            raise TypeError(f"expected str, not {type(path)!r}")
         if not path:
             raise ZipImportError('archive path is empty', path=path)
         if alt_path_sep:

Misc/NEWS.d/next/Library/2022-03-16-14-24-14.bpo-47025.qtT3CE.rst

@@ -0,0 +1 @@
+Drop support for :class:`bytes` on :attr:`sys.path`.