Suppress ValueError in fixup_namespace_packages. Fixes #520. Fixes #513.

CHANGES.rst

@@ -5,6 +5,9 @@ CHANGES
 v27.2.0
 -------
 
+* #520 and #513: Suppress ValueErrors in fixup_namespace_packages
+  when lookup fails.
+
 * Nicer, more consistent interfaces for msvc monkeypatching.
 
 v27.1.2

pkg_resources/__init__.py

@@ -2066,6 +2066,15 @@ def _rebuild_mod_path(orig_path, package_name, module):
     """
     sys_path = [_normalize_cached(p) for p in sys.path]
 
+    def safe_sys_path_index(entry):
+        """
+        Workaround for #520 and #513.
+        """
+        try:
+            return sys_path.index(entry)
+        except ValueError:
+            return float('inf')
+
     def position_in_sys_path(path):
         """
         Return the ordinal of the path based on its position in sys.path
@@ -2073,7 +2082,7 @@ def _rebuild_mod_path(orig_path, package_name, module):
         path_parts = path.split(os.sep)
         module_parts = package_name.count('.') + 1
         parts = path_parts[:-module_parts]
-        return sys_path.index(_normalize_cached(os.sep.join(parts)))
+        return safe_sys_path_index(_normalize_cached(os.sep.join(parts)))
 
     orig_path.sort(key=position_in_sys_path)
     module.__path__[:] = [_normalize_cached(p) for p in orig_path]