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.

[murchandamus]

I don’t see the point of this change. These python scripts accompany written specification documents as reference implementations, they are not living code. They are not expected to be updated, so they wouldn’t break. If someone were to add to these tests at a later time, and were to run into files not being loaded at that time, they could prompt an LLM to fix it as easily then.

Concept -0, I don’t think we should encourage this sort of code churn, but if you feel that it’s an improvement, please feel free to merge it, @jonatack.