BIP-0327: avoid using sys.path[0] to find current working directory

[omipheo]

Summary

bip-0327/reference.py and bip-0327/gen_vectors_helper.py both locate the test-vector JSON files via os.path.join(sys.path[0], 'vectors', '<file>.json'). As Sebastian Falbesoner noted in 4e18ee6 ("BIP-374: avoid using sys.path[0] to find current working directory"), this pattern is incompatible with any future sys.path.insert(0, ...) extension — for example, the sys.path.insert(0, str(Path(__file__).parent / "secp256k1lab/src")) shim that bip-0352 and bip-0374 use to locate their vendored secp256k1lab copies. Should bip-0327 follow the same vendoring pattern, every test-vector load would silently miss its file.

This PR switches both files to the Path(__file__).parent / 'vectors' / '...' pattern so the path is always resolved relative to the script itself, matching the BIP-374 precedent. import os and import sys are removed from reference.py (no remaining uses); gen_vectors_helper.py gets an explicit from pathlib import Path since it can no longer inherit those names through from reference import *.

Diff

Old call (×10 across 2 files)	New call
os.path.join(sys.path[0], 'vectors', 'X.json')	Path(__file__).parent / 'vectors' / 'X.json'

reference.py: 8 call sites (lines 499, 508, 532, 559, 577, 660, 717, 764). gen_vectors_helper.py: 2 call sites (lines 21, 49).
Imports adjusted to match.

Verification

$ python3 bip-0327/reference.py
$ echo $?
0

$ python3 bip-0327/gen_vectors_helper.py > /dev/null
$ echo $?
0

Both scripts continue to exit 0 with all test vectors loading.

(Note: bash bip-0327/tests.sh exits non-zero on master too — current local mypy versions flag four pre-existing bytearray/bytes mismatches at reference.py:354,355,671,672 that are unrelated to this PR. CI is presumably pinned to an older mypy; the runtime tests themselves pass on both branches.)

Notes

• Direct follow-up to 4e18ee6 ("BIP-374: avoid using sys.path[0]…").
  Same shape, same justification, applied to the next reference implementation in the same family.
• No behavior change beyond path-resolution robustness.

[jonatack]

ACK, it's a minor refactor but more idiomatic and robust and would serve as a better reference for developers.

[jonatack]

@omipheo note that BIPs 89, 328 and 340 also still use the same pattern. Maybe update them all here in one go.

[omipheo]

Done — pushed b39a896e28 extending the same fix to bip-0089/reference.py (8 sites), bip-0328/reference.py (1), and bip-0340/reference.py (1). Same pattern: os.path.join(sys.path[0], '...') → Path(__file__).parent / '...', with import os / import sys removed where they had no remaining uses.

Verified each script still runs clean:

$ for d in bip-0089 bip-0327 bip-0328 bip-0340; do (cd $d && python3 reference.py >/dev/null && echo "$d ok"); done
bip-0089 ok
bip-0327 ok
bip-0328 ok
bip-0340 ok

$ (cd bip-0327 && python3 gen_vectors_helper.py >/dev/null) && echo ok
ok

$ (cd bip-0340 && python3 test-vectors.py >/dev/null) && echo "test-vectors.py ok (wildcard importer of bip-0340/reference.py is unaffected by the os/sys removal — it imports sys itself for sys.stdout)"
test-vectors.py ok (wildcard importer of bip-0340/reference.py is unaffected by the os/sys removal — it imports sys itself for sys.stdout)

Happy to squash both commits into one if you'd prefer a single atomic change before merge.