pydantic_graph.persistence

SnapshotStatus module-attribute

SnapshotStatus = Literal[
    "created", "pending", "running", "success", "error"
]

The status of a snapshot.

• 'created': The snapshot has been created but not yet run.
• 'pending': The snapshot has been retrieved with load_next but not yet run.
• 'running': The snapshot is currently running.
• 'success': The snapshot has been run successfully.
• 'error': The snapshot has been run but an error occurred.

NodeSnapshot dataclass

Bases: Generic[StateT, RunEndT]

History step describing the execution of a node in a graph.

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

@dataclass
class NodeSnapshot(Generic[StateT, RunEndT]):
    """History step describing the execution of a node in a graph."""

    state: StateT
    """The state of the graph before the node is run."""
    node: Annotated[BaseNode[StateT, Any, RunEndT], _utils.CustomNodeSchema()]
    """The node to run next."""
    start_ts: datetime | None = None
    """The timestamp when the node started running, `None` until the run starts."""
    duration: float | None = None
    """The duration of the node run in seconds, if the node has been run."""
    status: SnapshotStatus = 'created'
    """The status of the snapshot."""
    kind: Literal['node'] = 'node'
    """The kind of history step, can be used as a discriminator when deserializing history."""

    id: str = UNSET_SNAPSHOT_ID
    """Unique ID of the snapshot."""

    def __post_init__(self) -> None:
        if self.id == UNSET_SNAPSHOT_ID:
            self.id = self.node.get_snapshot_id()

state instance-attribute

state: StateT

The state of the graph before the node is run.

node instance-attribute

node: Annotated[
    BaseNode[StateT, Any, RunEndT], CustomNodeSchema()
]

The node to run next.

start_ts class-attribute instance-attribute

start_ts: datetime | None = None

The timestamp when the node started running, None until the run starts.

duration class-attribute instance-attribute

duration: float | None = None

The duration of the node run in seconds, if the node has been run.

status class-attribute instance-attribute

status: SnapshotStatus = 'created'

The status of the snapshot.

kind class-attribute instance-attribute

kind: Literal['node'] = 'node'

The kind of history step, can be used as a discriminator when deserializing history.

id class-attribute instance-attribute

id: str = UNSET_SNAPSHOT_ID

Unique ID of the snapshot.

EndSnapshot dataclass

Bases: Generic[StateT, RunEndT]

History step describing the end of a graph run.

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

@dataclass
class EndSnapshot(Generic[StateT, RunEndT]):
    """History step describing the end of a graph run."""

    state: StateT
    """The state of the graph at the end of the run."""
    result: End[RunEndT]
    """The result of the graph run."""
    ts: datetime = field(default_factory=_utils.now_utc)
    """The timestamp when the graph run ended."""
    kind: Literal['end'] = 'end'
    """The kind of history step, can be used as a discriminator when deserializing history."""

    id: str = UNSET_SNAPSHOT_ID
    """Unique ID of the snapshot."""

    def __post_init__(self) -> None:
        if self.id == UNSET_SNAPSHOT_ID:
            self.id = self.node.get_snapshot_id()

    @property
    def node(self) -> End[RunEndT]:
        """Shim to get the [`result`][pydantic_graph.persistence.EndSnapshot.result].

        Useful to allow `[snapshot.node for snapshot in persistence.history]`.
        """
        return self.result

state instance-attribute

state: StateT

The state of the graph at the end of the run.

result instance-attribute

result: End[RunEndT]

The result of the graph run.

ts class-attribute instance-attribute

ts: datetime = field(default_factory=now_utc)

The timestamp when the graph run ended.

kind class-attribute instance-attribute

kind: Literal['end'] = 'end'

The kind of history step, can be used as a discriminator when deserializing history.

id class-attribute instance-attribute

id: str = UNSET_SNAPSHOT_ID

Unique ID of the snapshot.

node property

node: End[RunEndT]

Shim to get the result.

Useful to allow [snapshot.node for snapshot in persistence.history].

Snapshot module-attribute

Snapshot = Union[
    NodeSnapshot[StateT, RunEndT],
    EndSnapshot[StateT, RunEndT],
]

A step in the history of a graph run.

Graph.run returns a list of these steps describing the execution of the graph, together with the run return value.

BaseStatePersistence

Bases: ABC, Generic[StateT, RunEndT]

Abstract base class for storing the state of a graph run.

Each instance of a BaseStatePersistence subclass should be used for a single graph run.

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

class BaseStatePersistence(ABC, Generic[StateT, RunEndT]):
    """Abstract base class for storing the state of a graph run.

    Each instance of a `BaseStatePersistence` subclass should be used for a single graph run.
    """

    @abstractmethod
    async def snapshot_node(self, state: StateT, next_node: BaseNode[StateT, Any, RunEndT]) -> None:
        """Snapshot the state of a graph, when the next step is to run a node.

        This method should add a [`NodeSnapshot`][pydantic_graph.persistence.NodeSnapshot] to persistence.

        Args:
            state: The state of the graph.
            next_node: The next node to run.
        """
        raise NotImplementedError

    @abstractmethod
    async def snapshot_node_if_new(
        self, snapshot_id: str, state: StateT, next_node: BaseNode[StateT, Any, RunEndT]
    ) -> None:
        """Snapshot the state of a graph if the snapshot ID doesn't already exist in persistence.

        This method will generally call [`snapshot_node`][pydantic_graph.persistence.BaseStatePersistence.snapshot_node]
        but should do so in an atomic way.

        Args:
            snapshot_id: The ID of the snapshot to check.
            state: The state of the graph.
            next_node: The next node to run.
        """
        raise NotImplementedError

    @abstractmethod
    async def snapshot_end(self, state: StateT, end: End[RunEndT]) -> None:
        """Snapshot the state of a graph when the graph has ended.

        This method should add an [`EndSnapshot`][pydantic_graph.persistence.EndSnapshot] to persistence.

        Args:
            state: The state of the graph.
            end: data from the end of the run.
        """
        raise NotImplementedError

    @abstractmethod
    def record_run(self, snapshot_id: str) -> AbstractAsyncContextManager[None]:
        """Record the run of the node, or error if the node is already running.

        Args:
            snapshot_id: The ID of the snapshot to record.

        Raises:
            GraphNodeRunningError: if the node status it not `'created'` or `'pending'`.
            LookupError: if the snapshot ID is not found in persistence.

        Returns:
            An async context manager that records the run of the node.

        In particular this should set:

        - [`NodeSnapshot.status`][pydantic_graph.persistence.NodeSnapshot.status] to `'running'` and
          [`NodeSnapshot.start_ts`][pydantic_graph.persistence.NodeSnapshot.start_ts] when the run starts.
        - [`NodeSnapshot.status`][pydantic_graph.persistence.NodeSnapshot.status] to `'success'` or `'error'` and
          [`NodeSnapshot.duration`][pydantic_graph.persistence.NodeSnapshot.duration] when the run finishes.
        """
        raise NotImplementedError

    @abstractmethod
    async def load_next(self) -> NodeSnapshot[StateT, RunEndT] | None:
        """Retrieve a node snapshot with status `'created`' and set its status to `'pending'`.

        This is used by [`Graph.iter_from_persistence`][pydantic_graph.graph.Graph.iter_from_persistence]
        to get the next node to run.

        Returns: The snapshot, or `None` if no snapshot with status `'created`' exists.
        """
        raise NotImplementedError

    @abstractmethod
    async def load_all(self) -> list[Snapshot[StateT, RunEndT]]:
        """Load the entire history of snapshots.

        `load_all` is not used by pydantic-graph itself, instead it's provided to make it convenient to
        get all [snapshots][pydantic_graph.persistence.Snapshot] from persistence.

        Returns: The list of snapshots.
        """
        raise NotImplementedError

    def set_graph_types(self, graph: Graph[StateT, Any, RunEndT]) -> None:
        """Set the types of the state and run end from a graph.

        You generally won't need to customise this method, instead implement
        [`set_types`][pydantic_graph.persistence.BaseStatePersistence.set_types] and
        [`should_set_types`][pydantic_graph.persistence.BaseStatePersistence.should_set_types].
        """
        if self.should_set_types():
            with _utils.set_nodes_type_context(graph.get_nodes()):
                self.set_types(*graph.inferred_types)

    def should_set_types(self) -> bool:
        """Whether types need to be set.

        Implementations should override this method to return `True` when types have not been set if they are needed.
        """
        return False

    def set_types(self, state_type: type[StateT], run_end_type: type[RunEndT]) -> None:
        """Set the types of the state and run end.

        This can be used to create [type adapters][pydantic.TypeAdapter] for serializing and deserializing snapshots,
        e.g. with [`build_snapshot_list_type_adapter`][pydantic_graph.persistence.build_snapshot_list_type_adapter].

        Args:
            state_type: The state type.
            run_end_type: The run end type.
        """
        pass

snapshot_node abstractmethod async

snapshot_node(
    state: StateT, next_node: BaseNode[StateT, Any, RunEndT]
) -> None

Snapshot the state of a graph, when the next step is to run a node.

This method should add a NodeSnapshot to persistence.

Parameters:

Name	Type	Description	Default
state	StateT	The state of the graph.	required
next_node	BaseNode[StateT, Any, RunEndT]	The next node to run.	required

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

@abstractmethod
async def snapshot_node(self, state: StateT, next_node: BaseNode[StateT, Any, RunEndT]) -> None:
    """Snapshot the state of a graph, when the next step is to run a node.

    This method should add a [`NodeSnapshot`][pydantic_graph.persistence.NodeSnapshot] to persistence.

    Args:
        state: The state of the graph.
        next_node: The next node to run.
    """
    raise NotImplementedError

snapshot_node_if_new abstractmethod async

snapshot_node_if_new(
    snapshot_id: str,
    state: StateT,
    next_node: BaseNode[StateT, Any, RunEndT],
) -> None

Snapshot the state of a graph if the snapshot ID doesn't already exist in persistence.

This method will generally call snapshot_node but should do so in an atomic way.

Parameters:

Name	Type	Description	Default
snapshot_id	str	The ID of the snapshot to check.	required
state	StateT	The state of the graph.	required
next_node	BaseNode[StateT, Any, RunEndT]	The next node to run.	required

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

@abstractmethod
async def snapshot_node_if_new(
    self, snapshot_id: str, state: StateT, next_node: BaseNode[StateT, Any, RunEndT]
) -> None:
    """Snapshot the state of a graph if the snapshot ID doesn't already exist in persistence.

    This method will generally call [`snapshot_node`][pydantic_graph.persistence.BaseStatePersistence.snapshot_node]
    but should do so in an atomic way.

    Args:
        snapshot_id: The ID of the snapshot to check.
        state: The state of the graph.
        next_node: The next node to run.
    """
    raise NotImplementedError

snapshot_end abstractmethod async

snapshot_end(state: StateT, end: End[RunEndT]) -> None

Snapshot the state of a graph when the graph has ended.

This method should add an EndSnapshot to persistence.

Parameters:

Name	Type	Description	Default
state	StateT	The state of the graph.	required
end	End[RunEndT]	data from the end of the run.	required

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

@abstractmethod
async def snapshot_end(self, state: StateT, end: End[RunEndT]) -> None:
    """Snapshot the state of a graph when the graph has ended.

    This method should add an [`EndSnapshot`][pydantic_graph.persistence.EndSnapshot] to persistence.

    Args:
        state: The state of the graph.
        end: data from the end of the run.
    """
    raise NotImplementedError

record_run abstractmethod

record_run(
    snapshot_id: str,
) -> AbstractAsyncContextManager[None]

Record the run of the node, or error if the node is already running.

Parameters:

Name	Type	Description	Default
snapshot_id	str	The ID of the snapshot to record.	required

Raises:

Type	Description
GraphNodeRunningError	if the node status it not 'created' or 'pending'.
LookupError	if the snapshot ID is not found in persistence.

Returns:

Type	Description
AbstractAsyncContextManager[None]	An async context manager that records the run of the node.

In particular this should set:

• NodeSnapshot.status to 'running' and NodeSnapshot.start_ts when the run starts.
• NodeSnapshot.status to 'success' or 'error' and NodeSnapshot.duration when the run finishes.

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

@abstractmethod
def record_run(self, snapshot_id: str) -> AbstractAsyncContextManager[None]:
    """Record the run of the node, or error if the node is already running.

    Args:
        snapshot_id: The ID of the snapshot to record.

    Raises:
        GraphNodeRunningError: if the node status it not `'created'` or `'pending'`.
        LookupError: if the snapshot ID is not found in persistence.

    Returns:
        An async context manager that records the run of the node.

    In particular this should set:

    - [`NodeSnapshot.status`][pydantic_graph.persistence.NodeSnapshot.status] to `'running'` and
      [`NodeSnapshot.start_ts`][pydantic_graph.persistence.NodeSnapshot.start_ts] when the run starts.
    - [`NodeSnapshot.status`][pydantic_graph.persistence.NodeSnapshot.status] to `'success'` or `'error'` and
      [`NodeSnapshot.duration`][pydantic_graph.persistence.NodeSnapshot.duration] when the run finishes.
    """
    raise NotImplementedError

load_next abstractmethod async

load_next() -> NodeSnapshot[StateT, RunEndT] | None

Retrieve a node snapshot with status 'created' and set its status to 'pending'.

This is used by Graph.iter_from_persistence to get the next node to run.

Returns: The snapshot, or None if no snapshot with status 'created' exists.

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

@abstractmethod
async def load_next(self) -> NodeSnapshot[StateT, RunEndT] | None:
    """Retrieve a node snapshot with status `'created`' and set its status to `'pending'`.

    This is used by [`Graph.iter_from_persistence`][pydantic_graph.graph.Graph.iter_from_persistence]
    to get the next node to run.

    Returns: The snapshot, or `None` if no snapshot with status `'created`' exists.
    """
    raise NotImplementedError

load_all abstractmethod async

load_all() -> list[Snapshot[StateT, RunEndT]]

Load the entire history of snapshots.

load_all is not used by pydantic-graph itself, instead it's provided to make it convenient to get all snapshots from persistence.

Returns: The list of snapshots.

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

@abstractmethod
async def load_all(self) -> list[Snapshot[StateT, RunEndT]]:
    """Load the entire history of snapshots.

    `load_all` is not used by pydantic-graph itself, instead it's provided to make it convenient to
    get all [snapshots][pydantic_graph.persistence.Snapshot] from persistence.

    Returns: The list of snapshots.
    """
    raise NotImplementedError

set_graph_types

set_graph_types(graph: Graph[StateT, Any, RunEndT]) -> None

Set the types of the state and run end from a graph.

You generally won't need to customise this method, instead implement set_types and should_set_types.

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

def set_graph_types(self, graph: Graph[StateT, Any, RunEndT]) -> None:
    """Set the types of the state and run end from a graph.

    You generally won't need to customise this method, instead implement
    [`set_types`][pydantic_graph.persistence.BaseStatePersistence.set_types] and
    [`should_set_types`][pydantic_graph.persistence.BaseStatePersistence.should_set_types].
    """
    if self.should_set_types():
        with _utils.set_nodes_type_context(graph.get_nodes()):
            self.set_types(*graph.inferred_types)

should_set_types

should_set_types() -> bool

Whether types need to be set.

Implementations should override this method to return True when types have not been set if they are needed.

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

def should_set_types(self) -> bool:
    """Whether types need to be set.

    Implementations should override this method to return `True` when types have not been set if they are needed.
    """
    return False

set_types

set_types(
    state_type: type[StateT], run_end_type: type[RunEndT]
) -> None

Set the types of the state and run end.

This can be used to create type adapters for serializing and deserializing snapshots, e.g. with build_snapshot_list_type_adapter.

Parameters:

Name	Type	Description	Default
state_type	type[StateT]	The state type.	required
run_end_type	type[RunEndT]	The run end type.	required

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

def set_types(self, state_type: type[StateT], run_end_type: type[RunEndT]) -> None:
    """Set the types of the state and run end.

    This can be used to create [type adapters][pydantic.TypeAdapter] for serializing and deserializing snapshots,
    e.g. with [`build_snapshot_list_type_adapter`][pydantic_graph.persistence.build_snapshot_list_type_adapter].

    Args:
        state_type: The state type.
        run_end_type: The run end type.
    """
    pass

build_snapshot_list_type_adapter

build_snapshot_list_type_adapter(
    state_t: type[StateT], run_end_t: type[RunEndT]
) -> TypeAdapter[list[Snapshot[StateT, RunEndT]]]

Build a type adapter for a list of snapshots.

This method should be called from within set_types where context variables will be set such that Pydantic can create a schema for NodeSnapshot.node.

Source code in pydantic_graph/pydantic_graph/persistence/__init__.py

def build_snapshot_list_type_adapter(
    state_t: type[StateT], run_end_t: type[RunEndT]
) -> pydantic.TypeAdapter[list[Snapshot[StateT, RunEndT]]]:
    """Build a type adapter for a list of snapshots.

    This method should be called from within
    [`set_types`][pydantic_graph.persistence.BaseStatePersistence.set_types]
    where context variables will be set such that Pydantic can create a schema for
    [`NodeSnapshot.node`][pydantic_graph.persistence.NodeSnapshot.node].
    """
    return pydantic.TypeAdapter(list[Annotated[Snapshot[state_t, run_end_t], pydantic.Discriminator('kind')]])

In memory state persistence.

This module provides simple in memory state persistence for graphs.

SimpleStatePersistence dataclass

Bases: BaseStatePersistence[StateT, RunEndT]

Simple in memory state persistence that just hold the latest snapshot.

If no state persistence implementation is provided when running a graph, this is used by default.

Source code in pydantic_graph/pydantic_graph/persistence/in_mem.py

@dataclass
class SimpleStatePersistence(BaseStatePersistence[StateT, RunEndT]):
    """Simple in memory state persistence that just hold the latest snapshot.

    If no state persistence implementation is provided when running a graph, this is used by default.
    """

    last_snapshot: Snapshot[StateT, RunEndT] | None = None
    """The last snapshot."""

    async def snapshot_node(self, state: StateT, next_node: BaseNode[StateT, Any, RunEndT]) -> None:
        self.last_snapshot = NodeSnapshot(state=state, node=next_node)

    async def snapshot_node_if_new(
        self, snapshot_id: str, state: StateT, next_node: BaseNode[StateT, Any, RunEndT]
    ) -> None:
        if self.last_snapshot and self.last_snapshot.id == snapshot_id:
            return  # pragma: no cover
        else:
            await self.snapshot_node(state, next_node)

    async def snapshot_end(self, state: StateT, end: End[RunEndT]) -> None:
        self.last_snapshot = EndSnapshot(state=state, result=end)

    @asynccontextmanager
    async def record_run(self, snapshot_id: str) -> AsyncIterator[None]:
        if self.last_snapshot is None or snapshot_id != self.last_snapshot.id:
            raise LookupError(f'No snapshot found with id={snapshot_id!r}')

        assert isinstance(self.last_snapshot, NodeSnapshot), 'Only NodeSnapshot can be recorded'
        exceptions.GraphNodeStatusError.check(self.last_snapshot.status)
        self.last_snapshot.status = 'running'
        self.last_snapshot.start_ts = _utils.now_utc()

        start = perf_counter()
        try:
            yield
        except Exception:
            self.last_snapshot.duration = perf_counter() - start
            self.last_snapshot.status = 'error'
            raise
        else:
            self.last_snapshot.duration = perf_counter() - start
            self.last_snapshot.status = 'success'

    async def load_next(self) -> NodeSnapshot[StateT, RunEndT] | None:
        if isinstance(self.last_snapshot, NodeSnapshot) and self.last_snapshot.status == 'created':
            self.last_snapshot.status = 'pending'
            return self.last_snapshot

    async def load_all(self) -> list[Snapshot[StateT, RunEndT]]:
        raise NotImplementedError('load is not supported for SimpleStatePersistence')

last_snapshot class-attribute instance-attribute

last_snapshot: Snapshot[StateT, RunEndT] | None = None

The last snapshot.

FullStatePersistence dataclass

Bases: BaseStatePersistence[StateT, RunEndT]

In memory state persistence that hold a list of snapshots.

Source code in pydantic_graph/pydantic_graph/persistence/in_mem.py

@dataclass
class FullStatePersistence(BaseStatePersistence[StateT, RunEndT]):
    """In memory state persistence that hold a list of snapshots."""

    deep_copy: bool = True
    """Whether to deep copy the state and nodes when storing them.

    Defaults to `True` so even if nodes or state are modified after the snapshot is taken,
    the persistence history will record the value at the time of the snapshot.
    """
    history: list[Snapshot[StateT, RunEndT]] = field(default_factory=list)
    """List of snapshots taken during the graph run."""
    _snapshots_type_adapter: pydantic.TypeAdapter[list[Snapshot[StateT, RunEndT]]] | None = field(
        default=None, init=False, repr=False
    )

    async def snapshot_node(self, state: StateT, next_node: BaseNode[StateT, Any, RunEndT]) -> None:
        snapshot = NodeSnapshot(
            state=self._prep_state(state),
            node=next_node.deep_copy() if self.deep_copy else next_node,
        )
        self.history.append(snapshot)

    async def snapshot_node_if_new(
        self, snapshot_id: str, state: StateT, next_node: BaseNode[StateT, Any, RunEndT]
    ) -> None:
        if not any(s.id == snapshot_id for s in self.history):
            await self.snapshot_node(state, next_node)

    async def snapshot_end(self, state: StateT, end: End[RunEndT]) -> None:
        snapshot = EndSnapshot(
            state=self._prep_state(state),
            result=end.deep_copy_data() if self.deep_copy else end,
        )
        self.history.append(snapshot)

    @asynccontextmanager
    async def record_run(self, snapshot_id: str) -> AsyncIterator[None]:
        try:
            snapshot = next(s for s in self.history if s.id == snapshot_id)
        except StopIteration as e:
            raise LookupError(f'No snapshot found with id={snapshot_id!r}') from e

        assert isinstance(snapshot, NodeSnapshot), 'Only NodeSnapshot can be recorded'
        exceptions.GraphNodeStatusError.check(snapshot.status)
        snapshot.status = 'running'
        snapshot.start_ts = _utils.now_utc()
        start = perf_counter()
        try:
            yield
        except Exception:
            snapshot.duration = perf_counter() - start
            snapshot.status = 'error'
            raise
        else:
            snapshot.duration = perf_counter() - start
            snapshot.status = 'success'

    async def load_next(self) -> NodeSnapshot[StateT, RunEndT] | None:
        if snapshot := next((s for s in self.history if isinstance(s, NodeSnapshot) and s.status == 'created'), None):
            snapshot.status = 'pending'
            return snapshot

    async def load_all(self) -> list[Snapshot[StateT, RunEndT]]:
        return self.history

    def should_set_types(self) -> bool:
        return self._snapshots_type_adapter is None

    def set_types(self, state_type: type[StateT], run_end_type: type[RunEndT]) -> None:
        self._snapshots_type_adapter = build_snapshot_list_type_adapter(state_type, run_end_type)

    def dump_json(self, *, indent: int | None = None) -> bytes:
        """Dump the history to JSON bytes."""
        assert self._snapshots_type_adapter is not None, 'type adapter must be set to use `dump_json`'
        return self._snapshots_type_adapter.dump_json(self.history, indent=indent)

    def load_json(self, json_data: str | bytes | bytearray) -> None:
        """Load the history from JSON."""
        assert self._snapshots_type_adapter is not None, 'type adapter must be set to use `load_json`'
        self.history = self._snapshots_type_adapter.validate_json(json_data)

    def _prep_state(self, state: StateT) -> StateT:
        """Prepare state for snapshot, uses [`copy.deepcopy`][copy.deepcopy] by default."""
        if not self.deep_copy or state is None:
            return state
        else:
            return copy.deepcopy(state)

deep_copy class-attribute instance-attribute

deep_copy: bool = True

Whether to deep copy the state and nodes when storing them.

Defaults to True so even if nodes or state are modified after the snapshot is taken, the persistence history will record the value at the time of the snapshot.

history class-attribute instance-attribute

history: list[Snapshot[StateT, RunEndT]] = field(
    default_factory=list
)

List of snapshots taken during the graph run.

dump_json

dump_json(*, indent: int | None = None) -> bytes

Dump the history to JSON bytes.

Source code in pydantic_graph/pydantic_graph/persistence/in_mem.py

def dump_json(self, *, indent: int | None = None) -> bytes:
    """Dump the history to JSON bytes."""
    assert self._snapshots_type_adapter is not None, 'type adapter must be set to use `dump_json`'
    return self._snapshots_type_adapter.dump_json(self.history, indent=indent)

load_json

load_json(json_data: str | bytes | bytearray) -> None

Load the history from JSON.

Source code in pydantic_graph/pydantic_graph/persistence/in_mem.py

def load_json(self, json_data: str | bytes | bytearray) -> None:
    """Load the history from JSON."""
    assert self._snapshots_type_adapter is not None, 'type adapter must be set to use `load_json`'
    self.history = self._snapshots_type_adapter.validate_json(json_data)

FileStatePersistence dataclass

Bases: BaseStatePersistence[StateT, RunEndT]

File based state persistence that hold graph run state in a JSON file.

Source code in pydantic_graph/pydantic_graph/persistence/file.py

@dataclass
class FileStatePersistence(BaseStatePersistence[StateT, RunEndT]):
    """File based state persistence that hold graph run state in a JSON file."""

    json_file: Path
    """Path to the JSON file where the snapshots are stored.

    You should use a different file for each graph run, but a single file should be reused for multiple
    steps of the same run.

    For example if you have a run ID of the form `run_123abc`, you might create a `FileStatePersistence` thus:

    ```py
    from pathlib import Path

    from pydantic_graph import FullStatePersistence

    run_id = 'run_123abc'
    persistence = FullStatePersistence(Path('runs') / f'{run_id}.json')
    ```
    """
    _snapshots_type_adapter: pydantic.TypeAdapter[list[Snapshot[StateT, RunEndT]]] | None = field(
        default=None, init=False, repr=False
    )

    async def snapshot_node(self, state: StateT, next_node: BaseNode[StateT, Any, RunEndT]) -> None:
        await self._append_save(NodeSnapshot(state=state, node=next_node))

    async def snapshot_node_if_new(
        self, snapshot_id: str, state: StateT, next_node: BaseNode[StateT, Any, RunEndT]
    ) -> None:
        async with self._lock():
            snapshots = await self.load_all()
            if not any(s.id == snapshot_id for s in snapshots):  # pragma: no branch
                await self._append_save(NodeSnapshot(state=state, node=next_node), lock=False)

    async def snapshot_end(self, state: StateT, end: End[RunEndT]) -> None:
        await self._append_save(EndSnapshot(state=state, result=end))

    @asynccontextmanager
    async def record_run(self, snapshot_id: str) -> AsyncIterator[None]:
        async with self._lock():
            snapshots = await self.load_all()
            try:
                snapshot = next(s for s in snapshots if s.id == snapshot_id)
            except StopIteration as e:
                raise LookupError(f'No snapshot found with id={snapshot_id!r}') from e

            assert isinstance(snapshot, NodeSnapshot), 'Only NodeSnapshot can be recorded'
            exceptions.GraphNodeStatusError.check(snapshot.status)
            snapshot.status = 'running'
            snapshot.start_ts = _utils.now_utc()
            await self._save(snapshots)

        start = perf_counter()
        try:
            yield
        except Exception:
            duration = perf_counter() - start
            async with self._lock():
                await _graph_utils.run_in_executor(self._after_run_sync, snapshot_id, duration, 'error')
            raise
        else:
            snapshot.duration = perf_counter() - start
            async with self._lock():
                await _graph_utils.run_in_executor(self._after_run_sync, snapshot_id, snapshot.duration, 'success')

    async def load_next(self) -> NodeSnapshot[StateT, RunEndT] | None:
        async with self._lock():
            snapshots = await self.load_all()
            if snapshot := next((s for s in snapshots if isinstance(s, NodeSnapshot) and s.status == 'created'), None):
                snapshot.status = 'pending'
                await self._save(snapshots)
                return snapshot

    def should_set_types(self) -> bool:
        """Whether types need to be set."""
        return self._snapshots_type_adapter is None

    def set_types(self, state_type: type[StateT], run_end_type: type[RunEndT]) -> None:
        self._snapshots_type_adapter = build_snapshot_list_type_adapter(state_type, run_end_type)

    async def load_all(self) -> list[Snapshot[StateT, RunEndT]]:
        return await _graph_utils.run_in_executor(self._load_sync)

    def _load_sync(self) -> list[Snapshot[StateT, RunEndT]]:
        assert self._snapshots_type_adapter is not None, 'snapshots type adapter must be set'
        try:
            content = self.json_file.read_bytes()
        except FileNotFoundError:
            return []
        else:
            return self._snapshots_type_adapter.validate_json(content)

    def _after_run_sync(self, snapshot_id: str, duration: float, status: SnapshotStatus) -> None:
        snapshots = self._load_sync()
        snapshot = next(s for s in snapshots if s.id == snapshot_id)
        assert isinstance(snapshot, NodeSnapshot), 'Only NodeSnapshot can be recorded'
        snapshot.duration = duration
        snapshot.status = status
        self._save_sync(snapshots)

    async def _save(self, snapshots: list[Snapshot[StateT, RunEndT]]) -> None:
        await _graph_utils.run_in_executor(self._save_sync, snapshots)

    def _save_sync(self, snapshots: list[Snapshot[StateT, RunEndT]]) -> None:
        assert self._snapshots_type_adapter is not None, 'snapshots type adapter must be set'
        self.json_file.write_bytes(self._snapshots_type_adapter.dump_json(snapshots, indent=2))

    async def _append_save(self, snapshot: Snapshot[StateT, RunEndT], *, lock: bool = True) -> None:
        assert self._snapshots_type_adapter is not None, 'snapshots type adapter must be set'
        async with AsyncExitStack() as stack:
            if lock:
                await stack.enter_async_context(self._lock())
            snapshots = await self.load_all()
            snapshots.append(snapshot)
            await self._save(snapshots)

    @asynccontextmanager
    async def _lock(self, *, timeout: float = 1.0) -> AsyncIterator[None]:
        """Lock a file by checking and writing a `.pydantic-graph-persistence-lock` to it.

        Args:
            timeout: how long to wait for the lock

        Returns: an async context manager that holds the lock
        """
        lock_file = self.json_file.parent / f'{self.json_file.name}.pydantic-graph-persistence-lock'
        lock_id = secrets.token_urlsafe().encode()
        await asyncio.wait_for(_get_lock(lock_file, lock_id), timeout=timeout)
        try:
            yield
        finally:
            await _graph_utils.run_in_executor(lock_file.unlink, missing_ok=True)

json_file instance-attribute

json_file: Path

Path to the JSON file where the snapshots are stored.

You should use a different file for each graph run, but a single file should be reused for multiple steps of the same run.

For example if you have a run ID of the form run_123abc, you might create a FileStatePersistence thus:

from pathlib import Path

from pydantic_graph import FullStatePersistence

run_id = 'run_123abc'
persistence = FullStatePersistence(Path('runs') / f'{run_id}.json')

should_set_types

should_set_types() -> bool

Whether types need to be set.

Source code in pydantic_graph/pydantic_graph/persistence/file.py

def should_set_types(self) -> bool:
    """Whether types need to be set."""
    return self._snapshots_type_adapter is None