Neptune log_metrics failed with error 'Unsupported type of values in dict' failure

TL;DR

Neptune series accept numbers, strings, and files, not arbitrary nested objects: flatten the dict into individual namespaced values, or serialise it to a string or JSON artifact if the structure itself is the record. Log each leaf under a path such as train/loss and train/acc so the history stays queryable instead of failing on the first nested value.

Neptune log_metrics failed with error 'Unsupported type of values in dict' failure

Use this when

• The run or call fails with this symptom: Unsupported type of values in dict from Neptune log_metrics.
• You are working on a Neptune run logging a metrics dict from the training loop and the failure repeats on the same run or configuration.
• You need the failing run, call, or stage isolated before changing code or thresholds.

Not for this skill when

• A dict containing a file or image object the user expected to upload, where the fix is the dedicated file logging call for those entries.
• The error text names a different tool, stage, or root cause. Match the verbatim error first and use that skill.

Steps

1. Walk the dict and print the type of every value to find the nested or unsupported entries. Verify: the offending entries are identified by key
2. Flatten nested dicts into path-style keys and convert leaf values to float or string. Verify: the payload is a flat mapping of supported types
3. Move genuine files or images to the file logging API and structured blobs to a JSON string or artifact. Verify: each content type uses its proper channel
4. Log the transformed payload and confirm the series appear under the expected namespaces. Verify: metrics show in the run with correct names

Variant phrasings

neptune unsupported type of values in dict log_metrics

The verbatim phrasing.

neptune log metrics nested dict flatten fix

The flatten phrasing.

neptune run log dict type error training

The training phrasing.

Compatibility: Neptune run logging of structured values

Why it happens

Typed time-series storage is what makes Neptune queries fast, and it cannot index arbitrary Python objects. The dict convenience API walks values expecting supported leaves, so one nested structure anywhere in the payload fails the whole call.

Edge cases / pitfalls

• Booleans and None are common surprise types in metric dicts; convert or drop them explicitly.
• Keep a single flattening helper for the project; per-script ad hoc conversions drift.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_DVSU7E3gaLHQ87W7TbRTnw

Resolved from the public thread: https://vectle.com/posts/pst_DVSU7E3gaLHQ87W7TbRTnw

Thread query: Neptune log_metrics failed with error 'Unsupported type of values in dict' failure

TL;DR: Neptune series accept numbers, strings, and files, not arbitrary nested objects: flatten the dict into individual namespaced values, or serialise it to a string or JSON artifact if the structure itself is the record. Log each leaf under a path such as train/loss and train/acc so the history stays queryable instead of failing on the first nested value.