Container-method gaps: list.remove, list.index, list.copy, one-argument dict.pop

Found by sweeping every list and dict method against CPython. Everything else in both sweeps matched exactly — append, pop, pop(i), insert, count, extend, reverse, sort, clear, len, get, get with a default, dict.copy, keys, values, items, setdefault, in — so this is a short, well-bounded list.

d.pop("a", 0) (two arguments) works and is correct, so the one-argument form is a signature gap rather than a missing method: the parser requires the default. In CPython the one-argument form raises KeyError on a missing key and the two-argument form does not — which is the whole reason both exist.

All three fail loudly at compile time, so nothing silently computes a wrong answer. Filed as a feature.

list.index is a live wall. With the cross-module Callable fixes landed (242b96878, 33db0107d), songformatter's key analysis now matches CPython exactly, and of its five modules key_analysis, render_backend and settings all compile — convertrawtext.py and SongFormatter.py stop on exactly one line each:

pascal26:334: error: Nil Python: TPyList has no method index

That is the whole remaining distance to compiling the app, which is why this sits at 60 rather than 40.

str.index() is the same shape and is already reported by its own diagnostic (unsupported str method .index()); worth doing in the same pass since list.index and str.index share the semantics (raise when absent, unlike find, which returns -1).

Gate

make test-nilpy + self-host byte-identical, plus the list/dict method sweep diffed against CPython.

RESOLVED — four methods in pylib

• TPyList.index(v) — first element equal to v by PyVarEq, RAISING ValueError when absent, with CPython's exact wording (<repr> is not in list, the value itself, and deliberately different from remove's message).
• TPyList.remove(v) — same scan, then pop_at; ValueError when absent.
• TPyList.copy — a SHALLOW copy, like Python's: same element values, so appending to the copy leaves the original alone while a mutable element stays shared.
• TPyDict.pop(k) — the one-argument overload, raising KeyError. The two-arg form already existed; requiring the default is what made d.pop("a") a PARSE error rather than a missing method.

All four raise properly rather than halting, because [[bug-nilpy-runtime-raised-errors-bypass-try-except]] landed first — otherwise this would have added three more writeln + Halt sites.

Verified against CPython: index of a present and a duplicated element, remove of the first match, copy independence, and each of the four failure modes caught by its own exception type with matching message text.

The songformatter wall moved

Before: convertrawtext.py and SongFormatter.py both stopped at line 334, TPyList has no method index. Now both reach line 1198, and the wall there is a LIBRARY gap, not a compiler one:

Nil Python: PDFTextObject has no method setTextOrigin

That is the reportlab shim, so it belongs to Track B rather than N.

Gate

tools/gate.sh full.

Log

• 2026-07-30 — resolved, commit 8cef67f5c.