Add compatiblity mode

Include/internal/pycore_global_objects_fini_generated.h

@@ -1433,6 +1433,7 @@ _PyStaticObjects_CheckRefcnt(PyInterpreterState *interp) {
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__itruediv__));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__ixor__));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__lazy_import__));
+    _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__lazy_modules__));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__le__));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__len__));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(__length_hint__));
@@ -1851,7 +1852,6 @@ _PyStaticObjects_CheckRefcnt(PyInterpreterState *interp) {
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(last_type));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(last_value));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(latin1));
-    _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(lazy));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(leaf_size));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(legacy));
     _PyStaticObject_CheckRefcnt((PyObject *)&_Py_ID(len));

Include/internal/pycore_global_strings.h

@@ -156,6 +156,7 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(__itruediv__)
         STRUCT_FOR_ID(__ixor__)
         STRUCT_FOR_ID(__lazy_import__)
+        STRUCT_FOR_ID(__lazy_modules__)
         STRUCT_FOR_ID(__le__)
         STRUCT_FOR_ID(__len__)
         STRUCT_FOR_ID(__length_hint__)
@@ -574,7 +575,6 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(last_type)
         STRUCT_FOR_ID(last_value)
         STRUCT_FOR_ID(latin1)
-        STRUCT_FOR_ID(lazy)
         STRUCT_FOR_ID(leaf_size)
         STRUCT_FOR_ID(legacy)
         STRUCT_FOR_ID(len)

Include/internal/pycore_runtime_init_generated.h

@@ -1431,6 +1431,7 @@ extern "C" {
     INIT_ID(__itruediv__), \
     INIT_ID(__ixor__), \
     INIT_ID(__lazy_import__), \
+    INIT_ID(__lazy_modules__), \
     INIT_ID(__le__), \
     INIT_ID(__len__), \
     INIT_ID(__length_hint__), \
@@ -1849,7 +1850,6 @@ extern "C" {
     INIT_ID(last_type), \
     INIT_ID(last_value), \
     INIT_ID(latin1), \
-    INIT_ID(lazy), \
     INIT_ID(leaf_size), \
     INIT_ID(legacy), \
     INIT_ID(len), \

Include/internal/pycore_unicodeobject_generated.h

@@ -412,6 +412,10 @@ _PyUnicode_InitStaticStrings(PyInterpreterState *interp) {
     _PyUnicode_InternStatic(interp, &string);
     assert(_PyUnicode_CheckConsistency(string, 1));
     assert(PyUnicode_GET_LENGTH(string) != 1);
+    string = &_Py_ID(__lazy_modules__);
+    _PyUnicode_InternStatic(interp, &string);
+    assert(_PyUnicode_CheckConsistency(string, 1));
+    assert(PyUnicode_GET_LENGTH(string) != 1);
     string = &_Py_ID(__le__);
     _PyUnicode_InternStatic(interp, &string);
     assert(_PyUnicode_CheckConsistency(string, 1));
@@ -2084,10 +2088,6 @@ _PyUnicode_InitStaticStrings(PyInterpreterState *interp) {
     _PyUnicode_InternStatic(interp, &string);
     assert(_PyUnicode_CheckConsistency(string, 1));
     assert(PyUnicode_GET_LENGTH(string) != 1);
-    string = &_Py_ID(lazy);
-    _PyUnicode_InternStatic(interp, &string);
-    assert(_PyUnicode_CheckConsistency(string, 1));
-    assert(PyUnicode_GET_LENGTH(string) != 1);
     string = &_Py_ID(leaf_size);
     _PyUnicode_InternStatic(interp, &string);
     assert(_PyUnicode_CheckConsistency(string, 1));

Lib/test/test_import/__init__.py

@@ -2614,6 +2614,23 @@ def test_global_filter_from_true(self):
 
         self.assertFalse("test.test_import.data.lazy_imports.basic2" in sys.modules)
 
+    def test_compatibility_mode(self):
+        try:
+            import test.test_import.data.lazy_imports.basic_compatibility_mode
+        except ImportError as e:
+            self.fail('lazy import failed')
+
+        self.assertFalse("test.test_import.data.lazy_imports.basic2" in sys.modules)
+
+    def test_compatibility_mode_relative(self):
+        try:
+            import test.test_import.data.lazy_imports.basic_compatibility_mode_relative
+        except ImportError as e:
+            self.fail('lazy import failed')
+
+        self.assertFalse("test.test_import.data.lazy_imports.basic2" in sys.modules)
+
+
 
 class TestSinglePhaseSnapshot(ModuleSnapshot):
     """A representation of a single-phase init module for testing.

Lib/test/test_import/data/lazy_imports/basic_compatibility_mode.py

@@ -0,0 +1,2 @@
+__lazy_modules__ = ['test.test_import.data.lazy_imports.basic2']
+import test.test_import.data.lazy_imports.basic2

Lib/test/test_import/data/lazy_imports/basic_compatibility_mode_relative.py

@@ -0,0 +1,2 @@
+__lazy_modules__ = ['test.test_import.data.lazy_imports.basic2']
+lazy from .basic2 import f

Python/import.c

@@ -3862,6 +3862,7 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
     PyObject *final_mod = NULL;
     PyObject *mod = NULL;
     PyObject *package = NULL;
+    PyObject *lazy_modules = NULL;
     PyInterpreterState *interp = tstate->interp;
     int has_from;
 
@@ -3870,6 +3871,11 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
         goto error;
     }
 
+    if (globals != NULL &&
+        PyMapping_GetOptionalItem(globals, &_Py_ID(__lazy_modules__), &lazy_modules) < 0) {
+        goto error;
+    }
+
     /* The below code is importlib.__import__() & _gcd_import(), ported to C
        for added performance. */
 
@@ -3888,6 +3894,24 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
         goto error;
     }
 
+    if (lazy_modules != NULL) {
+        // Check and see if the module is opting in w/o syntax for backwards compatibility
+        // with older Python versions.
+        int contains = PySequence_Contains(lazy_modules, name);
+        if (contains < 0) {
+            goto error;
+        } else if (contains == 1) {
+            _PyInterpreterFrame *frame = _PyEval_GetFrame();
+            if (frame == NULL) {
+                PyErr_SetString(PyExc_RuntimeError, "no current frame");
+                goto error;
+            }
+            final_mod = _PyImport_LazyImportModuleLevelObject(tstate, name, frame->f_builtins, globals,
+                                                              locals, fromlist, level);
+            goto error;
+        }
+    }
+
     mod = import_get_module(tstate, abs_name);
     if (mod == NULL && _PyErr_Occurred(tstate)) {
         goto error;
@@ -3980,6 +4004,7 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *globals,
     }
 
   error:
+    Py_XDECREF(lazy_modules);
     Py_XDECREF(abs_name);
     Py_XDECREF(mod);
     Py_XDECREF(package);