Add a minimal reproduction for lazy loading issues

Author: lunaris

foo.py

@@ -0,0 +1,9 @@
+import sys
+import types
+
+class Foo(types.ModuleType):
+ @property
+ def bar(self) -> str:
+ return "Hello from foo.bar"
+
+sys.modules[__name__].__class__ = Foo

main.py

@@ -0,0 +1,33 @@
+import importlib.util
+import sys
+
+def lazy(fullname):
+ m = sys.modules.get(fullname, None)
+ if m is not None:
+ return m
+
+ spec = importlib.util.find_spec(fullname)
+
+ # Return early if find_spec has recursively called lazy_import
+ # again and pre-populated the sys.modules slot; an example of this
+ # is covered by test_lazy_import.
+ m = sys.modules.get(fullname, None)
+ if m is not None:
+ return m
+
+ loader = importlib.util.LazyLoader(spec.loader)
+ spec.loader = loader
+ module = importlib.util.module_from_spec(spec)
+
+ # Return early rather than overwriting the sys.modules slot.
+ m = sys.modules.get(fullname, None)
+ if m is not None:
+ return m
+
+ sys.modules[fullname] = module
+ loader.exec_module(module)
+ return module
+
+foo = lazy("foo")
+
+print(foo.bar)