Fix monkeypatch resolution of cached submodules

AUTHORS

@@ -351,6 +351,7 @@ Milan Lesnek
 minbang930
 Minh Dau
 Miro Hrončok
+Muhammad Sharif
 Mulat Mekonen
 mrbean-bremen
 Nathan Goldbaum

changelog/15157.bugfix.rst

@@ -0,0 +1,3 @@
+Fix string-based :meth:`pytest.MonkeyPatch.setattr` and
+:meth:`pytest.MonkeyPatch.delattr` for cached submodules whose attribute is missing
+from the parent package.

src/_pytest/monkeypatch.py

@@ -79,14 +79,13 @@ def resolve(name: str) -> object:
         # We use explicit un-nesting of the handling block in order
         # to avoid nested exceptions.
         try:
-            importlib.import_module(used)
+            found = importlib.import_module(used)
         except ImportError as ex:
             expected = str(ex).split()[-1]
             if expected == used:
                 raise
             else:
                 raise ImportError(f"import error in {used}: {ex}") from ex
-        found = annotated_getattr(found, part, used)
     return found
 
 

testing/test_monkeypatch.py

@@ -2,6 +2,7 @@
 from __future__ import annotations
 
 from collections.abc import Generator
+import importlib
 import os
 from pathlib import Path
 import re
@@ -53,6 +54,29 @@ class A:
 
 
 class TestSetattrWithImportPath:
+    @pytest.mark.parametrize("operation", ["setattr", "delattr"])
+    def test_cached_module_without_parent_attribute(
+        self, pytester: Pytester, monkeypatch: MonkeyPatch, operation: str
+    ) -> None:
+        package_path = pytester.mkdir("cached_target_package")
+        (package_path / "__init__.py").write_text("", encoding="utf-8")
+        (package_path / "child.py").write_text("value = 1", encoding="utf-8")
+        monkeypatch.syspath_prepend(str(pytester.path))
+        child = importlib.import_module("cached_target_package.child")
+        package = importlib.import_module("cached_target_package")
+        monkeypatch.delattr(package, "child")
+
+        # A cached module is still importable without its parent attribute.
+        assert importlib.import_module("cached_target_package.child") is child
+        with monkeypatch.context() as mp:
+            if operation == "setattr":
+                mp.setattr("cached_target_package.child.value", 2)
+                assert child.value == 2
+            else:
+                mp.delattr("cached_target_package.child.value")
+                assert not hasattr(child, "value")
+        assert child.value == 1
+
     def test_string_expression(self, monkeypatch: MonkeyPatch) -> None:
         with monkeypatch.context() as mp:
             mp.setattr("os.path.abspath", lambda x: "hello2")