More conservative interpretation of PathFinder failures

Follow up to pylint-dev#1536

astroid/interpreter/_import/util.py

@@ -6,16 +6,24 @@
 
 import pathlib
 import sys
-from functools import lru_cache
 from importlib._bootstrap_external import _NamespacePath
 from importlib.util import _find_spec_from_path
 
 
-@lru_cache(maxsize=4096)
 def is_namespace(modname: str) -> bool:
     if modname in sys.builtin_module_names:
         return False
 
+    try:
+        if sys.modules[modname].__spec__ is None and modname != "__main__":
+            return True
+    except KeyError:
+        pass
+    except AttributeError:
+        # work around for "py" library:
+        # https://github.com/pytest-dev/apipkg/issues/13
+        return False
+
     found_spec = None
 
     # find_spec() attempts to import parent packages when given dotted paths.
@@ -34,8 +42,7 @@ def is_namespace(modname: str) -> bool:
                 working_modname, path=last_submodule_search_locations
             )
         except ValueError:
-            # Assume it's a .pth file, unless it's __main__
-            return modname != "__main__"
+            return False
         except KeyError:
             # Intermediate steps might raise KeyErrors
             # https://github.com/python/cpython/issues/93334

astroid/manager.py

@@ -18,7 +18,7 @@
 
 from astroid.const import BRAIN_MODULES_DIRECTORY
 from astroid.exceptions import AstroidBuildingError, AstroidImportError
-from astroid.interpreter._import import spec, util
+from astroid.interpreter._import import spec
 from astroid.modutils import (
     NoSourceFile,
     _cache_normalize_path_,
@@ -384,7 +384,6 @@ def clear_cache(self) -> None:
         for lru_cache in (
             LookupMixIn.lookup,
             _cache_normalize_path_,
-            util.is_namespace,
             ObjectModel.attributes,
         ):
             lru_cache.cache_clear()

tests/unittest_manager.py

@@ -334,7 +334,6 @@ def test_clear_cache_clears_other_lru_caches(self) -> None:
         lrus = (
             astroid.nodes.node_classes.LookupMixIn.lookup,
             astroid.modutils._cache_normalize_path_,
-            util.is_namespace,
             astroid.interpreter.objectmodel.ObjectModel.attributes,
         )
 
@@ -344,7 +343,6 @@ def test_clear_cache_clears_other_lru_caches(self) -> None:
         # Generate some hits and misses
         ClassDef().lookup("garbage")
         is_standard_module("unittest", std_path=["garbage_path"])
-        util.is_namespace("unittest")
         astroid.interpreter.objectmodel.ObjectModel().attributes()
 
         # Did the hits or misses actually happen?