Implement Flow state export method (#2134)

This commit implements a method for exporting the state of a flow into a
JSON-serializable dictionary.

The idea is producing a human-readable version of state that can be
inspected or consumed by other systems, hence JSON and not pickling or
marshalling.

I consider it an export because it's a one-way process, meaning it
cannot be loaded back into Python because of complex types.

src/crewai/flow/state_utils.py

@@ -0,0 +1,52 @@
+from datetime import date, datetime
+from typing import Any
+
+from pydantic import BaseModel
+
+from crewai.flow import Flow
+
+
+def export_state(flow: Flow) -> dict[str, Any]:
+    """Exports the Flow's internal state as JSON-compatible data structures.
+
+    Performs a one-way transformation of a Flow's state into basic Python types
+    that can be safely serialized to JSON. To prevent infinite recursion with
+    circular references, the conversion is limited to a depth of 5 levels.
+
+    Args:
+        flow: The Flow object whose state needs to be exported
+
+    Returns:
+        dict[str, Any]: The transformed state using JSON-compatible Python
+            types.
+    """
+    return _to_serializable(flow._state)
+
+
+def _to_serializable(obj: Any, max_depth: int = 5, _current_depth: int = 0) -> Any:
+    if _current_depth >= max_depth:
+        return repr(obj)
+
+    if isinstance(obj, (str, int, float, bool, type(None))):
+        return obj
+    elif isinstance(obj, (date, datetime)):
+        return obj.isoformat()
+    elif isinstance(obj, (list, tuple, set)):
+        return [_to_serializable(item, max_depth, _current_depth + 1) for item in obj]
+    elif isinstance(obj, dict):
+        return {
+            _to_serializable_key(key): _to_serializable(
+                value, max_depth, _current_depth + 1
+            )
+            for key, value in obj.items()
+        }
+    elif isinstance(obj, BaseModel):
+        return _to_serializable(obj.model_dump(), max_depth, _current_depth + 1)
+    else:
+        return repr(obj)
+
+
+def _to_serializable_key(key: Any) -> str:
+    if isinstance(key, (str, int)):
+        return str(key)
+    return f"key_{id(key)}_{repr(key)}"

tests/flow/test_state_utils.py

@@ -0,0 +1,156 @@
+from datetime import date, datetime
+from typing import List
+from unittest.mock import Mock
+
+import pytest
+from pydantic import BaseModel
+
+from crewai.flow import Flow
+from crewai.flow.state_utils import export_state
+
+
+class Address(BaseModel):
+    street: str
+    city: str
+    country: str
+
+
+class Person(BaseModel):
+    name: str
+    age: int
+    address: Address
+    birthday: date
+    skills: List[str]
+
+
+@pytest.fixture
+def mock_flow():
+    def create_flow(state):
+        flow = Mock(spec=Flow)
+        flow._state = state
+        return flow
+
+    return create_flow
+
+
+@pytest.mark.parametrize(
+    "test_input,expected",
+    [
+        ({"text": "hello world"}, {"text": "hello world"}),
+        ({"number": 42}, {"number": 42}),
+        ({"decimal": 3.14}, {"decimal": 3.14}),
+        ({"flag": True}, {"flag": True}),
+        ({"empty": None}, {"empty": None}),
+        ({"list": [1, 2, 3]}, {"list": [1, 2, 3]}),
+        ({"tuple": (1, 2, 3)}, {"tuple": [1, 2, 3]}),
+        ({"set": {1, 2, 3}}, {"set": [1, 2, 3]}),
+        ({"nested": [1, [2, 3], {4, 5}]}, {"nested": [1, [2, 3], [4, 5]]}),
+    ],
+)
+def test_basic_serialization(mock_flow, test_input, expected):
+    flow = mock_flow(test_input)
+    result = export_state(flow)
+    assert result == expected
+
+
+@pytest.mark.parametrize(
+    "input_date,expected",
+    [
+        (date(2024, 1, 1), "2024-01-01"),
+        (datetime(2024, 1, 1, 12, 30), "2024-01-01T12:30:00"),
+    ],
+)
+def test_temporal_serialization(mock_flow, input_date, expected):
+    flow = mock_flow({"date": input_date})
+    result = export_state(flow)
+    assert result["date"] == expected
+
+
+@pytest.mark.parametrize(
+    "key,value,expected_key_type",
+    [
+        (("tuple", "key"), "value", str),
+        (None, "value", str),
+        (123, "value", str),
+        ("normal", "value", str),
+    ],
+)
+def test_dictionary_key_serialization(mock_flow, key, value, expected_key_type):
+    flow = mock_flow({key: value})
+    result = export_state(flow)
+    assert len(result) == 1
+    result_key = next(iter(result.keys()))
+    assert isinstance(result_key, expected_key_type)
+    assert result[result_key] == value
+
+
+@pytest.mark.parametrize(
+    "callable_obj,expected_in_result",
+    [
+        (lambda x: x * 2, "lambda"),
+        (str.upper, "upper"),
+    ],
+)
+def test_callable_serialization(mock_flow, callable_obj, expected_in_result):
+    flow = mock_flow({"func": callable_obj})
+    result = export_state(flow)
+    assert isinstance(result["func"], str)
+    assert expected_in_result in result["func"].lower()
+
+
+def test_pydantic_model_serialization(mock_flow):
+    address = Address(street="123 Main St", city="Tech City", country="Pythonia")
+
+    person = Person(
+        name="John Doe",
+        age=30,
+        address=address,
+        birthday=date(1994, 1, 1),
+        skills=["Python", "Testing"],
+    )
+
+    flow = mock_flow(
+        {
+            "single_model": address,
+            "nested_model": person,
+            "model_list": [address, address],
+            "model_dict": {"home": address},
+        }
+    )
+
+    result = export_state(flow)
+
+    assert result["single_model"]["street"] == "123 Main St"
+
+    assert result["nested_model"]["name"] == "John Doe"
+    assert result["nested_model"]["address"]["city"] == "Tech City"
+    assert result["nested_model"]["birthday"] == "1994-01-01"
+
+    assert len(result["model_list"]) == 2
+    assert all(m["street"] == "123 Main St" for m in result["model_list"])
+    assert result["model_dict"]["home"]["city"] == "Tech City"
+
+
+def test_depth_limit(mock_flow):
+    """Test max depth handling with a deeply nested structure"""
+
+    def create_nested(depth):
+        if depth == 0:
+            return "value"
+        return {"next": create_nested(depth - 1)}
+
+    deep_structure = create_nested(10)
+    flow = mock_flow(deep_structure)
+    result = export_state(flow)
+
+    assert result == {
+        "next": {
+            "next": {
+                "next": {
+                    "next": {
+                        "next": "{'next': {'next': {'next': {'next': {'next': 'value'}}}}}"
+                    }
+                }
+            }
+        }
+    }