[GSoC 2025] Saving and Loading Custom Models

[medha-14]

Description

PR to serialise and deserialise custom models

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #)

Important checks:

Please confirm the following before marking the PR as ready for review:

• No style issues: nox -s pre-commit
• All tests pass: nox -s tests
• The documentation builds: nox -s doctests
• Code is commented for hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

❌ Patch coverage is 99.22179% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.86%. Comparing base (e154fec) to head (9db6435).
⚠️ Report is 161 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/pybamm/expression_tree/operations/serialise.py	99.21%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5056      +/-   ##
===========================================
- Coverage    98.86%   98.86%   -0.01%     
===========================================
  Files          320      320              
  Lines        26568    26825     +257     
===========================================
+ Hits         26266    26520     +254     
- Misses         302      305       +3     

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[medha-14]

I’ve added an example notebook to demonstrate how the functionality works. I’d appreciate any suggestions for improvements or refinements you might have.

[agriyakhetarpal]

Thank you! We are getting closer. Could you please add a CHANGELOG entry and give this PR a more descriptive title, now that we know its scope?

I've left some suggestions related to the tests, that should be addressed (better error matching + better ways to organise saving/deleting files across tests)

Also, I had a question about the structure of the JSON. Right now, we have it as:

{
  "schema_version": "1.0",
  "pybamm_version": 25.6
  "name": "MyModel",
  "rhs": [], # something
  "algebraic": [], # something
  "initial_conditions": [], # something
  # ...
}

Would it be better organised if we were to have it as

{
  "schema_version": "1.0",
  "pybamm_version": 25.6
  model: {
  "name": "MyModel",
  "rhs": [], # something
  "algebraic": [], # something
  "initial_conditions": [], # something
  # ...
  }
}

i.e., have it nested, so that the schema version, the PyBaMM version, and the model are at one level and the model's attributes are one level deeper?

[Saransh-cpp]

This looks good to me now! Should be ready to merge once Agriya's comment above is resolved.

[medha-14]

I have addressed all the reviews. Please review and let me know if any further changes are needed.

[agriyakhetarpal]

Great work! I only have some nits and one functional change to request.

[Saransh-cpp]

Should be ready to merge once @valentinsulzer approves it 🚀

[agriyakhetarpal]

Hmm, I'm unsure if the macOS-3.10 test failure is related. Just re-triggered it...