Added JSON serialisation for Lambda functions

[bennthomsen]

Pull Request Summary

Title: Added JSON serialization for Lambda functions

Description

This PR adds support for serializing and deserializing BluePrint objects that contain arbitrary functions (arb_func), including lambda functions and named functions, to/from JSON format.

Changes

Files Modified:

• src/broadbean/blueprint.py (+131 lines) - Core serialization/deserialization logic
• tests/test_arb_func_serialization.py (+263 lines) - New comprehensive test suite
• tests/test_blueprint.py (+1 line) - Updated existing test

Key Features

1. Lambda Function Serialization: Lambda functions used with PulseAtoms.arb_func can now be serialized to JSON by storing their source code, extracted using inspect.getsource() with regex parsing.

2. Named Function Serialization: Regular named functions are serialized with both their name and full source code, allowing reconstruction even in different Python sessions.

3. Graceful Fallbacks: When functions cannot be reconstructed (e.g., missing dependencies or invalid source), the system falls back to a zero function with appropriate warnings.

4. Sample Rate Persistence: The SR (sample rate) property is now included in the blueprint description and restored during deserialization.

5. Backward Compatibility: Legacy JSON formats without the new func_type field are still supported.

Usage Example

import broadbean as bb
import numpy as np

# Create a blueprint with a lambda function using arb_func
bp = bb.BluePrint()

# Add a segment using arb_func with a lambda function
my_lambda = lambda t, **kwargs: np.sin(2 * np.pi * kwargs.get('freq', 1) * t)
bp.insertSegment(
    0, 
    bb.PulseAtoms.arb_func, 
    args=(my_lambda, {'freq': 10}),  # (function, kwargs_dict)
    name='sine_wave',
    dur=1e-6
)
bp.setSR(1e9)

# Serialize to JSON file
bp.write_to_json('my_blueprint.json')

# Later, reconstruct the blueprint from JSON
bp_restored = bb.BluePrint.init_from_json('my_blueprint.json')

# The lambda function is reconstructed and works as expected
print(bp_restored.description)

Example with a named function:

import broadbean as bb
import numpy as np

# Define a custom waveform function
def gaussian_pulse(t, **kwargs):
    amplitude = kwargs.get('amplitude', 1.0)
    sigma = kwargs.get('sigma', 1e-7)
    center = kwargs.get('center', 5e-7)
    return amplitude * np.exp(-((t - center) ** 2) / (2 * sigma ** 2))

# Create blueprint
bp = bb.BluePrint()
bp.insertSegment(
    0,
    bb.PulseAtoms.arb_func,
    args=(gaussian_pulse, {'amplitude': 0.5, 'sigma': 2e-7, 'center': 5e-7}),
    name='gaussian',
    dur=1e-6
)
bp.setSR(1e9)

# Save and restore
bp.write_to_json('gaussian_blueprint.json')
bp_restored = bb.BluePrint.init_from_json('gaussian_blueprint.json')

Technical Details

Serialization (description property):

• Detects arb_func segments and extracts function information
• For lambdas: extracts source code using regex to isolate the lambda expression
• For named functions: stores both function name and complete source code
• Stores associated kwargs dictionary

Deserialization (blueprint_from_description):

• Reconstructs lambda functions using eval()
• Reconstructs named functions by executing source code in isolated namespace
• Falls back to global namespace lookup or zero function if reconstruction fails

Testing

Added comprehensive test suite (test_arb_func_serialization.py) covering:

• Lambda function serialization round-trip
• Named function serialization round-trip
• Complex expressions with numpy operations
• Kwargs preservation
• JSON file write/read operations
• Error handling and fallbacks
• Integration with existing blueprint functionality

Breaking Changes

None - existing functionality and JSON format remains compatible.

[codecov]

Codecov Report

❌ Patch coverage is 42.42424% with 38 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.16%. Comparing base (ee22118) to head (93d64c2).

Files with missing lines	Patch %	Lines
src/broadbean/blueprint.py	42.42%	38 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1695      +/-   ##
==========================================
- Coverage   72.12%   71.16%   -0.97%     
==========================================
  Files           9        9              
  Lines        1539     1602      +63     
==========================================
+ Hits         1110     1140      +30     
- Misses        429      462      +33     

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[astafan8]

why are there two duplicated(?) plots instead of one in this example? or is it github mis-rendering?

[bennthomsen]

This seems to be working fine in VScode.