[Hardik K (hardikkaurani)]

Description

Fixes #2931.

QCoDeS provides NumpyJSONEncoder to support serialization of types that Python's standard json module cannot handle out of the box, such as complex numbers (encoded as {"__dtype__": "complex", "re": ..., "im": ...}) and uncertainties.UFloat objects (encoded as {"__dtype__": "UFloat", "nominal_value": ..., "std_dev": ...}).

However, there was no corresponding decoder class to reconstruct these objects when reading JSON data back. Users decoding serialized dictionaries were left with raw dictionaries containing __dtype__ keys instead of restored Python objects.

This PR introduces NumpyJSONDecoder as a subclass of json.JSONDecoder with a default object_hook that recognizes these encoded structures and restores them into their corresponding Python types:

• Objects with __dtype__ == "complex" and "re", "im" fields are converted back to Python complex.
• Objects with __dtype__ == "UFloat" and "nominal_value", "std_dev" fields are converted back to uncertainties.ufloat.
• Custom object_hook arguments can still be passed to customize or chain decoding logic.
• Standard JSON values, strings, lists, numbers, and plain dictionaries decode untouched.

Testing

Added comprehensive unit tests to tests/helpers/test_json_encoder.py:

• test_numpy_json_decoder_complex: Verifies decoding and type restoration for complex numbers.
• test_numpy_json_decoder_ufloat: Verifies roundtrip restoration of uncertainties.ufloat.
• test_numpy_json_decoder_roundtrip_examplemetadata: Verifies decoding of complex numbers and plain types in the standard EXAMPLEMETADATA structure.
• test_numpy_json_decoder_custom_object_hook: Verifies user-provided object_hook customization.

All 17 tests in tests/helpers/test_json_encoder.py pass cleanly. ruff check and ruff format are clean across all modified files.

[Hardik K (hardikkaurani)]

Hello Mikhail Astafev (@astafan8),

I have submitted this pull request to resolve issue #2931 by providing a dedicated NumpyJSONDecoder class to complement NumpyJSONEncoder.

The decoder inspects encoded dictionary payloads and restores complex and uncertainties.UFloat instances from their serialized representations while allowing custom object_hook chaining and leaving standard JSON primitives untouched.

Unit tests covering typed roundtrips, custom hooks, and existing metadata examples have been added to tests/helpers/test_json_encoder.py, with all tests and formatting checks passing cleanly. Please review when convenient. Thank you for your time.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.59%. Comparing base (3d24a6a) to head (9ace8cb).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8623      +/-   ##
==========================================
+ Coverage   72.58%   72.59%   +0.01%     
==========================================
  Files         307      307              
  Lines       32409    32422      +13     
==========================================
+ Hits        23525    23538      +13     
  Misses       8884     8884              

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[Hardik K (hardikkaurani)]

Hi Jens Hedegaard Nielsen (@jenshnielsen),

Could you please take a look at this PR when you have a moment? It adds NumpyJSONDecoder to complement NumpyJSONEncoder (resolving #2931) for restoring complex and uncertainties.UFloat serialized objects.

All CI matrix jobs (pytest, mypy, docs, pre-commit, codecov) have passed across Python 3.12–3.15 on Linux and Windows. Thank you for your time!