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__getattr__ (dynamic attribute fallback) is not supported

class C:
    def __getattr__(self, name):
        return "GETATTR-" + name

print(C().missing_thing)    # CPython: GETATTR-missing_thing



pascal26:4: error: "missing_thing": no such member on this record/class

Re-measured at HEAD 2026-08-09: unchanged.

Why this is the largest of the three siblings

Attribute lookup is resolved STATICALLY against the class layout, and the whole point of __getattr__ is to answer for names that are not in it. So the miss has to become a runtime call rather than a compile error — which means the compile-time "no such member" diagnostic can no longer fire for a class that declares __getattr__, and every member-access site has to agree on that.

Note the existing pydynattr_get/pydynattr_set store: NilPy already has a runtime attribute path for names it cannot resolve statically. Whether __getattr__ should be layered on top of that (dynattr miss → __getattr__) is the design question to settle first, and CPython's own order is the answer to match: instance dict, then class, then __getattr__ last.

Do not weaken the static diagnostic for classes that do NOT declare __getattr__. A typo'd attribute becoming a silent runtime miss is a much worse trade than the feature is worth; the whole point is that the fallback is opt-in per class.

__setattr__/__delattr__ are the same family and should be scoped with it.

Gate

.npy diffed against CPython: a class with __getattr__ answering for a missing name, a REAL attribute still winning over it, and the control that a class WITHOUT __getattr__ still gets the compile-time "no such member" error.

Resolution (2026-08-15)

The ticket's own diagnosis was a session out of date, and re-measuring first is what made this a small change instead of the frontend project it describes. c.missing already compiled — the miss reaches pydynattr_get at run time, which raised AttributeError rather than consulting the dunder. So most of the work was in pylib, not in the resolver.

PyUserObjGetattr is the dispatcher, reading the call shape from the RTTI the way the other dunder callers do: __getattr__'s name parameter is a str, but the unannotated def __getattr__(self, name) types it as a Variant, so both parameter shapes are dispatched and the return fans over the six RetKinds. PyUserObjGetattrTry is the same call with an AttributeError refusal turned into False, which is what a PRESENCE question needs — CPython defines hasattr as "getattr does not raise", so a dunder that refuses some names has to be RUN to answer it.

Wired at every place attribute lookup can miss, which was the real work:

The sibling found on the way, and fixed with it

D().missing refused at COMPILE time ("missing": no such member) while d = D(); d.missing resolved at run time — the receiver-shape split again (member access has two parsers, and only the lvalue one knew). That is not specific to __getattr__: Plain().b refused to compile where CPython raises AttributeError at run time, so try: obj.maybe / except AttributeError: could not even build for a call-result receiver. The chained-selector arm now routes an unresolved member on a user class to the runtime getter for any NilPy class, matching what the bare-identifier spelling always did.

Cost accepted, stated rather than hidden

getattr(o, n, default) lowers to has ? get : default, so a class whose __getattr__ has SIDE EFFECTS sees two calls where CPython makes one. The value is right either way. Collapsing it needs a single pydynattr_get_or runtime entry and a lowering change; not done here.

Not covered

hasattr on a builtin container or a str still answers False for a method it plainly has (hasattr([1], "append")). Pre-existing — the pinned compiler says False for all three — and unrelated to the dunder; filed as [[bug-nilpy-hasattr-on-a-builtin-container-or-str-answers-false]].

Test: test/test_nilpy_getattr_dunder.npy, byte-identical to CPython — the declared members winning, both receiver shapes, inheritance, hasattr/getattr including a computed name, a dunder that refuses, a dunder returning a callable and being called, and a class WITHOUT the dunder still raising. The eleven attribute-related sibling tests re-run green.

Log