fix(metrics): import compute_reward_score so image_reward stops raising NameError

[Anai-Guo]

Problem

cache-dit-metrics-cli image_reward ... can never succeed — it dies with a NameError before it reaches any model code.

src/cache_dit/metrics/metrics.py binds the per-image helper, but the only call site unpacks the directory-level function, which is never imported:

# metrics.py:24-25
compute_clip_score       = _safe_import(".clip_score",   "compute_clip_score")
compute_reward_score_img = _safe_import(".image_reward", "compute_reward_score_img")

# metrics.py:659-663
if metric == "clip_score":
    clip_score, n = compute_clip_score(img_test, prompt_true)      # ok
    _logging_msg(clip_score, "clip_score", n)
if metric == "image_reward":
    image_reward, n = compute_reward_score(img_test, prompt_true)  # NameError
    _logging_msg(image_reward, "image_reward", n)

compute_reward_score is not defined in this module, and the name that is bound — compute_reward_score_img — is referenced nowhere in the tree (grep -rn compute_reward_score_img returns only line 25).

setup.cfg's flake8 ignore list contains F821, so the undefined name never showed up in CI.

Fix

Bind the same shape the working clip_score sibling uses — one line, no behaviour change anywhere else:

-compute_reward_score_img = _safe_import(".image_reward", "compute_reward_score_img")
+compute_reward_score = _safe_import(".image_reward", "compute_reward_score")

This is not just a naming slip: the two functions have different contracts, and only the dir-level one fits the call site.

name	signature	returns	fits a, n = f(...)?
compute_reward_score (dir)	(img_dir, prompts, imagereward_model_path=None)	Tuple[float, int]	✅
compute_reward_score_img (per-image)	(img, prompt, imagereward_model_path=None)	float	❌ TypeError on unpack

For reference, clip_score.py exposes the exact same pair (compute_clip_score / compute_clip_score_img) and metrics.py already imports the dir-level one there.

Verification

Ran the real CLI entrypoint against a throwaway image dir + prompt file (only the unrelated third-party diffusers / ImageReward imports are stubbed on this box; all cache_dit code is the unmodified repo source).

Before

compute_clip_score       -> <function compute_clip_score>
compute_reward_score_img -> <function import_error_metric_func>
compute_reward_score     -> <MISSING>
RESULT: NameError: name 'compute_reward_score' is not defined
        raised at metrics.py:662 | image_reward, n = compute_reward_score(img_test, prompt_true)

After

compute_clip_score       -> <function compute_clip_score>
compute_reward_score_img -> <MISSING>
compute_reward_score     -> <function import_error_metric_func>
RESULT: ImportError: This metric function requires additional dependencies that are
        not installed. Please check the documentation for installation instructions.

i.e. the call now resolves and reaches _safe_import's intended, actionable error for a
missing optional dep instead of a bare NameError. With ImageReward importable, the
name binds to the real dir-level function whose signature matches compute_clip_score's
one-for-one:

metrics.compute_clip_score   -> cache_dit.metrics.clip_score.compute_clip_score
    (img_dir, prompts, clip_model_path=None) -> Union[Tuple[float, int], Tuple[None, None]]
metrics.compute_reward_score -> cache_dit.metrics.image_reward.compute_reward_score
    (img_dir, prompts, imagereward_model_path=None) -> Union[Tuple[float, int], Tuple[None, None]]

Lint (pinned to the versions in .pre-commit-config.yaml):

• yapf==0.40.2 --diff src/cache_dit/metrics/metrics.py → no diff
• flake8==7.1.1 --config=setup.cfg → unchanged from main (only pre-existing D1xx docstring notices)
• python -m pyflakes src/ → no undefined name remaining

🤖 Generated with Claude Code

[Copilot]

🟢 Approval recommended

The targeted import now matches the call site’s expected function name and return contract.

Pull request overview

Fixes the image_reward CLI path by importing the directory-level function used by the existing call site.

Changes:

• Replaces the unused per-image helper binding with compute_reward_score.
• Prevents the NameError and preserves optional-dependency handling.

File summaries

File	Description
src/cache_dit/metrics/metrics.py	Corrects the ImageReward function binding.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Balanced

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[DefTruth]

LGTM, thanks for this fix!