pythongh-113356: Ignore errors in "._ABC.pth"

On macOS the system can create a "._" file next to a
regular file when the system needs to store metadata
that is not supported by the filesystem (such as storing
extended attributes on an exFAT filesystem).

Those files are binary data and cause startup failures when
the base file is a ".pth" file.

Lib/site.py

@@ -176,29 +176,40 @@ def addpackage(sitedir, name, known_paths):
     except OSError:
         return
     with f:
-        for n, line in enumerate(f):
-            if line.startswith("#"):
-                continue
-            if line.strip() == "":
-                continue
-            try:
-                if line.startswith(("import ", "import\t")):
-                    exec(line)
+        try:
+            for n, line in enumerate(f):
+                if line.startswith("#"):
                     continue
-                line = line.rstrip()
-                dir, dircase = makepath(sitedir, line)
-                if not dircase in known_paths and os.path.exists(dir):
-                    sys.path.append(dir)
-                    known_paths.add(dircase)
-            except Exception as exc:
-                print("Error processing line {:d} of {}:\n".format(n+1, fullname),
-                      file=sys.stderr)
-                import traceback
-                for record in traceback.format_exception(exc):
-                    for line in record.splitlines():
-                        print('  '+line, file=sys.stderr)
-                print("\nRemainder of file ignored", file=sys.stderr)
-                break
+                if line.strip() == "":
+                    continue
+                try:
+                    if line.startswith(("import ", "import\t")):
+                        exec(line)
+                        continue
+                    line = line.rstrip()
+                    dir, dircase = makepath(sitedir, line)
+                    if not dircase in known_paths and os.path.exists(dir):
+                        sys.path.append(dir)
+                        known_paths.add(dircase)
+                except Exception as exc:
+                    print("Error processing line {:d} of {}:\n".format(n+1, fullname),
+                          file=sys.stderr)
+                    import traceback
+                    for record in traceback.format_exception(exc):
+                        for line in record.splitlines():
+                            print('  '+line, file=sys.stderr)
+                    print("\nRemainder of file ignored", file=sys.stderr)
+                    break
+        except UnicodeDecodeError:
+            # MacOS can create files with a "._" prefix in the name
+            # next to the regular file when the system needs to store
+            # metadata (such as extended attributes) that the filesystem
+            # cannot store natively.
+            #
+            # Ignore errors when trying to parse these files.
+            if name.startswith("._") and os.path.exists(os.path.join(sitedir, name[2:])):
+                return
+            raise
     if reset:
         known_paths = None
     return known_paths

Lib/test/test_site.py

@@ -181,6 +181,20 @@ def test_addpackage_import_bad_pth_file(self):
             if isinstance(path, str):
                 self.assertNotIn("abc\x00def", path)
 
+    def test_addpackage_macOS_resources(self):
+        # GH-113356
+        pth_dir, pth_fn = self.make_pth("dummy\n")
+        resource_fork = os.path.join(pth_dir, "._" + pth_fn)
+        with open(resource_fork, "wb") as fp:
+            self.addCleanup(lambda: os.remove(resource_fork))
+            # Some random that that isn't valid UTF-8
+            fp.write(b"\xff\xff\xff")
+
+        with captured_stderr() as err_out:
+            self.assertFalse(site.addpackage(pth_dir, "._" + pth_fn, set()))
+        self.assertEqual(err_out.getvalue(), "")
+
+
     def test_addsitedir(self):
         # Same tests for test_addpackage since addsitedir() essentially just
         # calls addpackage() for every .pth file in the directory

Misc/NEWS.d/next/macOS/2023-12-21-14-18-24.gh-issue-113356.Vz2osH.rst

@@ -0,0 +1,3 @@
+Ignore "._" prefixed pth files when those cannot be parsed. These files are
+created on macOS when the system tries store metadata that is not supported
+by the filesystem (such as extended attributes on exFAT)