py/objtype: Avoid crash on calling members of uninitialized native type.

When subclassing a native type, calling native members in `__init__` before
`super().__init__()` has been called could cause a crash.  In this
situation, `self` in `mp_convert_member_lookup` is the
`native_base_init_wrapper_obj`.  The check added in this commit ensures
that an `AttributeError` is raised before this happens, which is consistent
with other failed lookups.

Also fix a typo in a related comment.

Signed-off-by: Laurens Valk <laurens@pybricks.com>

1 files changed, 37 insertions, 0 deletions

diff --git a/tests/misc/cexample_subclass.py b/tests/misc/cexample_subclass.py
new file mode 100644
index 0000000000..9f52a2c737
--- /dev/null
+++ b/tests/misc/cexample_subclass.py
@@ -0,0 +1,37 @@
+# test subclassing custom native class
+
+try:
+    from cexample import AdvancedTimer
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+
+class SubTimer(AdvancedTimer):
+    def __init__(self):
+        # At this point, self does not yet represent a AdvancedTimer instance.
+        print(self)
+
+        # So lookups via type.attr handler will fail.
+        try:
+            self.seconds
+        except AttributeError:
+            print("AttributeError")
+
+        # Also applies to builtin methods.
+        try:
+            self.time()
+        except AttributeError:
+            print("AttributeError")
+
+        # Initialize base class.
+        super().__init__(self)
+
+        # Now you can access methods and attributes normally.
+        self.time()
+        print(self.seconds)
+        self.seconds = 123
+        print(self.seconds)
+
+
+watch = SubTimer()