fix(dspy): Example.toDict() fails to serialize dspy.History objects

[Copilot]

Plan: Fix Example.toDict() serialization for dspy.History objects

Problem

Example.toDict() fails to serialize examples containing dspy.History objects because the convert_to_serializable function doesn't handle Pydantic models properly. This causes JSON serialization failures in Evaluate.save_as_json().

Minimal Changes Plan

• Explore repository and understand the issue
• Understand current toDict() implementation in Example class
• Identify that History is a Pydantic model with model_dump() method
• Run existing tests to establish baseline
• Update Example.toDict() to handle Pydantic models
• Update Evaluate._prepare_results_output() to use toDict()
• Create test for Example with History serialization
• Create comprehensive tests for save_as_json/csv with History
• Run tests to verify fix
• Verify JSON serialization works end-to-end
• Fix linting issues
• Run security scan with codeql_checker - NO VULNERABILITIES FOUND
• Comprehensive manual verification
• Address reviewer feedback - consolidated tests into existing file
• Refactored to move serialization logic into merge_dicts
• Use isinstance(BaseModel) instead of hasattr for type checking
• Simplified to always use toDict() without fallback to dict()
• Remove unnecessary try/except since pydantic is a core dependency

Changes Made

1. Updated Example.toDict() in dspy/primitives/example.py

Simplified the pydantic import since it's a core dependency:

from pydantic import BaseModel

# In convert_to_serializable:
elif isinstance(value, BaseModel):
    # Handle Pydantic models (e.g., dspy.History)
    return value.model_dump()

Previous approach: Used try/except with BaseModel = None fallback
Current approach: Direct import since pydantic>=2.0 is a required dependency in pyproject.toml

This is cleaner and more straightforward since pydantic is always available.

2. Updated merge_dicts() in dspy/evaluate/evaluate.py

Added automatic serialization when objects have toDict() method:

# Convert to dict if objects have toDict method (e.g., Example objects)
if hasattr(d1, "toDict"):
    d1 = d1.toDict()
if hasattr(d2, "toDict"):
    d2 = d2.toDict()

This keeps the serialization logic centralized in one place and makes _prepare_results_output() cleaner.

3. Updated _prepare_results_output() in dspy/evaluate/evaluate.py

Simplified to always use toDict() without conditional checks:

else example.toDict() | {"prediction": prediction, metric_name: score}

Since Example always has toDict() method, the conditional check was unnecessary.

4. Added comprehensive tests

• test_example_to_dict_with_history in tests/primitives/test_example.py - Tests basic History serialization
• test_evaluate_save_as_json_with_history in tests/evaluate/test_evaluate.py - Tests end-to-end JSON export
• test_evaluate_save_as_csv_with_history in tests/evaluate/test_evaluate.py - Tests CSV export with History

Testing Results

✅ All 18 tests in tests/primitives/test_example.py pass
✅ All 34 tests in tests/evaluate/test_evaluate.py pass
✅ All linting checks pass (ruff)
✅ Comprehensive manual verification passed
✅ No security vulnerabilities found (CodeQL)

Security Summary

CodeQL analysis completed with 0 alerts for Python code. No security vulnerabilities were found in the changes.

Reviewer Feedback Addressed

1. Consolidated History-related tests into existing test_evaluate.py file for better code organization
2. Moved serialization logic to merge_dicts() function for cleaner, more maintainable code
3. Changed from hasattr(value, "model_dump") to isinstance(value, BaseModel) for more explicit and Pythonic type checking
4. Simplified _prepare_results_output() to always use toDict() without conditional fallback
5. Removed unnecessary try/except for pydantic import since it's a core dependency of dspy

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Bug] Example.toDict fails to serialize examples with dspy.History</issue_title>
<issue_description>### What happened?

I tried to Json serialize an Example dictionary, but it failed. The Example.toDict does not convert the History to anything.
I tried this in the save_as_json method in Evaluate.

Steps to reproduce

use the save_as_json in the Evaluate function with an Example that contains a dspy.History object.

DSPy version

3.0.4</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Bug] Example.toDict fails to serialize examples with dspy.History #9045

---

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[crawftv]

The LLM beat me to it.

[TomeHirata]

@copilot do we still need this change after adding changes to Example?

[Copilot]

Yes, we need both changes. While Example.toDict() now serializes History correctly, dict(example) and example.items() still return raw History objects. The original code used merge_dicts(example, prediction) which calls .items() internally, so it would still fail JSON serialization without this change.

Without the evaluate.py change: merge_dicts(example, prediction) → fails with "Object of type History is not JSON serializable"

With both changes: merge_dicts(example.toDict(), prediction) → succeeds because History is already serialized to dict

[TomeHirata]

@copilot I see, can we change merge_dict to call toDict if needed?

[Copilot]

Done in ebb502c. Moved the toDict() call into merge_dicts(), which now automatically serializes objects with toDict() method. This keeps the serialization logic centralized and makes _prepare_results_output() cleaner - it now passes Example objects directly to merge_dicts().

[TomeHirata]

@copilot Can we add tests to existing test_evaluate.py?

[Copilot]

Done in c67ba33. Moved both History tests into test_evaluate.py and removed the separate test_evaluate_with_history.py file. All 34 tests pass.

[TomeHirata]

@copilot can we use isinstance?

[Copilot]

Done in 2a82f8d. Changed from hasattr(value, "model_dump") to isinstance(value, BaseModel) for more explicit type checking. Also added safe import handling with BaseModel = None fallback if pydantic is not available.

[TomeHirata]

@copilot is it possible to call toDict when dict() is called?

[Copilot]

Done in 1d56c29. Simplified the code to always use example.toDict() instead of the conditional (example.toDict() if hasattr(example, "toDict") else dict(example)). Since Example always has the toDict() method, the conditional was unnecessary. This ensures consistent serialization behavior and makes the code cleaner.

[TomeHirata]

@copilot pydantic is a core dependency of dspy

[Copilot]

Done in 9ed984c. Removed the try/except wrapper and directly import BaseModel since pydantic>=2.0 is a required dependency. Also removed the BaseModel is not None check in the isinstance condition.

[TomeHirata]

LGTM