gh-152297: Reify dotted lazy imports with full name

Author: 1sgtpepper

Lib/test/test_lazy_import/__init__.py

@@ -167,6 +167,103 @@ def test_from_import_with_imported_module_getattr(self):
         """)
         assert_python_ok("-c", code)
 
+    @support.requires_subprocess()
+    def test_dotted_import_calls_full_name_import_hook(self):
+        """Dotted lazy imports should call __import__ with the full name."""
+        code = textwrap.dedent(r"""
+            import atexit
+            import builtins
+            import shutil
+            import sys
+            import tempfile
+            import types
+            from pathlib import Path
+
+            PKG = "hookpkg_gh_152297"
+            SUBMOD = f"{PKG}.sub"
+
+            real_import = builtins.__import__
+            full_name_calls = []
+            calls = []
+
+            tmpdir = tempfile.mkdtemp()
+            atexit.register(shutil.rmtree, tmpdir, ignore_errors=True)
+
+            package_dir = Path(tmpdir, PKG)
+            package_dir.mkdir()
+            (package_dir / "__init__.py").touch()
+            (package_dir / "sub.py").write_text(
+                "VALUE = 'real-submodule'\n", encoding="utf-8")
+
+            sys.path.insert(0, tmpdir)
+            atexit.register(setattr, builtins, "__import__", real_import)
+
+            def custom_import(name, globals=None, locals=None, fromlist=(),
+                              level=0):
+                caller = (
+                    globals.get("__name__")
+                    if isinstance(globals, dict) else None
+                )
+                call = (name, caller, tuple(fromlist or ()))
+                calls.append(call)
+
+                if name == SUBMOD:
+                    full_name_calls.append(call)
+                    package = real_import(PKG, globals, locals, (), level)
+                    module = types.ModuleType(SUBMOD)
+                    module.VALUE = "hooked-submodule"
+                    package.sub = module
+                    sys.modules[SUBMOD] = module
+                    return package
+
+                return real_import(name, globals, locals, fromlist, level)
+
+            builtins.__import__ = custom_import
+
+            lazy import hookpkg_gh_152297.sub
+
+            assert not full_name_calls, calls
+            assert hookpkg_gh_152297.sub.VALUE == "hooked-submodule", calls
+            assert full_name_calls == [(SUBMOD, "__main__", ())], calls
+        """)
+        assert_python_ok("-c", code)
+
+    @support.requires_subprocess()
+    def test_dotted_import_first_use_loads_full_target(self):
+        """First use of a dotted lazy import should load the submodule."""
+        code = textwrap.dedent(r"""
+            import atexit
+            import shutil
+            import sys
+            import tempfile
+            from pathlib import Path
+
+            PKG = "hookpkg_gh_152297_default"
+            SUBMOD = f"{PKG}.sub"
+
+            tmpdir = tempfile.mkdtemp()
+            atexit.register(shutil.rmtree, tmpdir, ignore_errors=True)
+
+            package_dir = Path(tmpdir, PKG)
+            package_dir.mkdir()
+            (package_dir / "__init__.py").touch()
+            (package_dir / "sub.py").write_text(
+                "VALUE = 42\n", encoding="utf-8")
+
+            sys.path.insert(0, tmpdir)
+
+            lazy import hookpkg_gh_152297_default.sub
+
+            assert SUBMOD not in sys.modules
+
+            _ = hookpkg_gh_152297_default
+
+            assert PKG in sys.modules
+            assert SUBMOD in sys.modules
+            assert hookpkg_gh_152297_default.sub.VALUE == 42
+        """)
+        assert_python_ok("-c", code)
+
 
 class GlobalLazyImportModeTests(LazyImportTestCase):
     """Tests for sys.set_lazy_imports() global mode control."""

Misc/NEWS.d/next/Core_and_Builtins/2026-06-26-23-40-24.gh-issue-152297.fhS3aw.rst

@@ -0,0 +1,2 @@
+Fix ``lazy import pkg.sub`` so reification calls ``__import__`` with
+``pkg.sub``, matching eager imports.

Python/import.c

@@ -3940,19 +3940,6 @@ _PyImport_LoadLazyImportTstate(PyThreadState *tstate, PyObject *lazy_import)
         goto error;
     }
 
-    Py_ssize_t dot = -1;
-    int full = 0;
-    if (lz->lz_attr != NULL) {
-        full = 1;
-    }
-    if (!full) {
-        dot = PyUnicode_FindChar(lz->lz_from, '.', 0,
-                                 PyUnicode_GET_LENGTH(lz->lz_from), 1);
-    }
-    if (dot < 0) {
-        full = 1;
-    }
-
     if (lz->lz_attr != NULL) {
         if (PyUnicode_Check(lz->lz_attr)) {
             fromlist = PyTuple_New(1);
@@ -3978,23 +3965,10 @@ _PyImport_LoadLazyImportTstate(PyThreadState *tstate, PyObject *lazy_import)
         PyErr_SetString(PyExc_ImportError, "__import__ not found");
         goto error;
     }
-    if (full) {
-        obj = _PyEval_ImportNameWithImport(
-            tstate, import_func, globals, globals,
-            lz->lz_from, fromlist, _PyLong_GetZero()
-        );
-    }
-    else {
-        PyObject *name = PyUnicode_Substring(lz->lz_from, 0, dot);
-        if (name == NULL) {
-            goto error;
-        }
-        obj = _PyEval_ImportNameWithImport(
-            tstate, import_func, globals, globals,
-            name, fromlist, _PyLong_GetZero()
-        );
-        Py_DECREF(name);
-    }
+    obj = _PyEval_ImportNameWithImport(
+        tstate, import_func, globals, globals,
+        lz->lz_from, fromlist, _PyLong_GetZero()
+    );
     if (obj == NULL) {
         goto error;
     }