GH-134872: add ModuleNotFoundError suggestions

Doc/library/importlib.rst

@@ -275,6 +275,16 @@ ABC hierarchy::
       .. versionchanged:: 3.4
          Returns ``None`` when called instead of :data:`NotImplemented`.
 
+   .. method:: discover(parent=None)
+
+      An optional method which searches for possible specs with given *parent*
+      module spec. If *parent* is *None*, :meth:`PathEntryFinder.discover` will
+      search for top-level modules.
+
+      Returns an iterable of possible specs.
+
+      .. versionadded:: next
+
 
 .. class:: PathEntryFinder
 
@@ -307,6 +317,16 @@ ABC hierarchy::
       :meth:`importlib.machinery.PathFinder.invalidate_caches`
       when invalidating the caches of all cached finders.
 
+   .. method:: discover(parent=None)
+
+      An optional method which searches for possible specs with given *parent*
+      module spec. If *parent* is *None*, :meth:`PathEntryFinder.discover` will
+      search for top-level modules.
+
+      Returns an iterable of possible specs.
+
+      .. versionadded:: next
+
 
 .. class:: Loader
 

Lib/importlib/_bootstrap_external.py

@@ -1323,6 +1323,21 @@ def find_spec(cls, fullname, path=None, target=None):
         else:
             return spec
 
+    @classmethod
+    def discover(cls, parent=None):
+        if parent is None:
+            path = sys.path
+        else:
+            path = parent.submodule_search_locations
+
+        for entry in path:
+            if not isinstance(entry, str):
+                continue
+            if (finder := cls._path_importer_cache(entry)) is None:
+                continue
+            if discover := getattr(finder, 'discover', None):
+                yield from discover(parent)
+
     @staticmethod
     def find_distributions(*args, **kwargs):
         """
@@ -1472,6 +1487,27 @@ def path_hook_for_FileFinder(path):
 
         return path_hook_for_FileFinder
 
+    def _find_children(self):
+        for entry in _os.scandir(self.path):
+            if entry.name == _PYCACHE:
+                continue
+            # packages
+            if entry.is_dir() and '.' not in entry.name:
+                yield entry.name
+            # files
+            if entry.is_file():
+                yield from [
+                    entry.name.removesuffix(suffix)
+                    for suffix, _ in self._loaders
+                    if entry.name.endswith(suffix)
+                ]
+
+    def discover(self, parent=None):
+        module_prefix = f'{parent.name}.' if parent else ''
+        for child_name in self._find_children():
+            if spec := self.find_spec(module_prefix + child_name):
+                yield spec
+
     def __repr__(self):
         return f'FileFinder({self.path!r})'
 

Lib/importlib/abc.py

@@ -45,6 +45,15 @@ def invalidate_caches(self):
         This method is used by importlib.invalidate_caches().
         """
 
+    def discover(self, parent=None):
+        """An optional method which searches for possible specs with given *parent*.
+        If *parent* is *None*, MetaPathFinder.discover will search for top-level modules.
+
+        Returns an iterable of possible specs.
+        """
+        return ()
+
+
 _register(MetaPathFinder, machinery.BuiltinImporter, machinery.FrozenImporter,
           machinery.PathFinder, machinery.WindowsRegistryFinder)
 
@@ -58,6 +67,14 @@ def invalidate_caches(self):
         This method is used by PathFinder.invalidate_caches().
         """
 
+    def discover(self, parent=None):
+        """An optional method which searches for possible specs with given *parent*.
+        If *parent* is *None*, PathEntryFinder.discover will search for top-level modules.
+
+        Returns an iterable of possible specs.
+        """
+        return ()
+
 _register(PathEntryFinder, machinery.FileFinder)
 
 

Lib/traceback.py

@@ -10,6 +10,7 @@
 import keyword
 import tokenize
 import io
+import importlib.util
 import _colorize
 
 from contextlib import suppress
@@ -1124,6 +1125,10 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
                 self._str += (". Site initialization is disabled, did you forget to "
                     + "add the site-packages directory to sys.path "
                     + "or to enable your virtual environment?")
+            else:
+                suggestion = _compute_suggestion_error(exc_value, exc_traceback, module_name)
+                if suggestion:
+                    self._str += f". Did you mean: '{suggestion}'?"
         elif exc_type and issubclass(exc_type, (NameError, AttributeError)) and \
                 getattr(exc_value, "name", None) is not None:
             wrong_name = getattr(exc_value, "name", None)
@@ -1672,6 +1677,18 @@ def _compute_suggestion_error(exc_value, tb, wrong_name):
                 d = [x for x in d if x[:1] != '_']
         except Exception:
             return None
+    elif isinstance(exc_value, ModuleNotFoundError):
+        try:
+            if parent_name := wrong_name.rpartition('.')[0]:
+                parent = importlib.util.find_spec(parent_name)
+            else:
+                parent = None
+            d = []
+            for finder in sys.meta_path:
+                if discover := getattr(finder, 'discover', None):
+                    d += [spec.name for spec in discover(parent)]
+        except Exception:
+            return None
     elif isinstance(exc_value, ImportError):
         try:
             mod = __import__(exc_value.name)

Misc/NEWS.d/next/Library/2025-10-10-14-08-58.gh-issue-139899.09leRY.rst

@@ -0,0 +1,2 @@
+Introduced :meth:`MetaPathFinder.discover` and
+:meth:`PathEntryFinder.discover`.