An action with `NDArray` return type doesn't work over HTTP

Open

#231 opened on Dec 18, 2025 3 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 3/5
Estimated time: 1-2 days
Newbie friendliness: 45/100

Issue type: Bug
Clarity: Mostly clear
Activity status: Stale
Tech stack: fastapi, numpy, python
Domain: api, backend

Research direction

Start with the unit test added in #230 and trace the HTTP response serialization path for an action returning NDArray. The work is done when the test passes and NDArray responses serialize over HTTP in the same way as ArrayModel responses.

Written by the indexing model from the issue text.

Description

bug

Describe the bug
An action with NDArray return type doesn't work over HTTP. It throws a the following error

pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize unknown type: <class 'numpy.ndarray'>

ArrayModel can be used, but then it is typehinted incorrectly when called on the server

To Reproduce
See unit test added in #230

Expected behaviour
It serialises just as ArrayModel would.

System:

OS: Kubuntu 24.04
Python version. 3.11
Version. 0.0.13

Dominant language: Python
Stars: 9
Forks: 4
PR merge metrics: No merged PRs in 30d

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