pymc-devs/pymc

Check idata dims/coords for consistency before sampling begins

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#7,891 opened on Aug 8, 2025

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 (11 comments) (1 reaction) (0 assignees)Python (1,902 forks)batch import
beginner friendlyhackathonhelp wantedmaintenanceshape problem

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Description

Description

This is a painful gotcha I get hit by once in a while. If you have inconsistencies between the model coords and variable shapes, PyMC will still happy sample (often for hours, ask me how I know), then error out when it gets to the final step of building the idata.

I don't think there needs to be complex logic to validate static shapes etc, I'm thinking we could do a smoke test on the model initial point (or a single prior draw) to make sure it can be converted to an idata, and raise before sampling if not.

Contributor guide

Research direction
Implement a smoke test that attempts to convert the model initial point or a single prior draw to an InferenceData object, catching any inconsistencies and raising an error before sampling begins.
Tech stack
python
Domain
data
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Python
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60