Flow and branches¶

Declare the edges between nodes and route by the state. See Graphs and flow.

Name	What it is
Start, end and edges
`START`	The entry of a flow: `START >> node` names the first node of a graph.
`END`	The end of a flow: `node >> END`, a branch target, or a `goto` target.
`FlowStartEdge`	Edge from `START` to the first node.
`FlowEdge`	Static edge between two nodes, written as `a >> b`.
`FlowBranchEdge`	Conditional edge, written as `a >> branch(...)`.
`StartSentinel`	Marker for the entry of a graph flow, used as `START >> node`.
`EndSentinel`	Marker for the end of a graph flow.
Branches
`branch`	Route to one of several targets by a key computed from the state.
`when`	Route to `target` when a predicate holds, else to `otherwise`.
`FlowBranch`	Conditional routing table produced by `branch` or `when`.

Start, end and edges¶

The entry of a flow: START >> node names the first node of a graph.

The end of a flow: node >> END, a branch target, or a goto target.

FlowStartEdge(target)

Edge from START to the first node.

Attributes
`target`	`Node`

FlowEdge(source, target)

Static edge between two nodes, written as a >> b.

Attributes
`source`	`Node`
`target`	`Node \| EndSentinel`

FlowBranchEdge(source, branch)

Conditional edge, written as a >> branch(...).

Attributes
`source`	`Node`
`branch`	`FlowBranch`

Marker for the entry of a graph flow, used as START >> node.

Marker for the end of a graph flow.

branch(router, mapping, *, ref=None) -> FlowBranch

Route to one of several targets by a key computed from the state.

Parameters
`router`	`Callable[[Any], Any]`	Receives the state and returns a key of `mapping`, matched by equality. Any other key raises `GraphExecutionError` at run time.
`mapping`	`Mapping[Any, Node \| EndSentinel]`	Router keys to target nodes or `END`.
`ref`	`str \| None`	Import path of the router, for `Graph.to_spec`.

Raises
`TypeError`	If `router` is not callable.
`GraphConfigError`	If `mapping` is empty.

when(predicate, target, *, otherwise) -> FlowBranch

Route to target when a predicate holds, else to otherwise.

Parameters
`predicate`	`Callable[[Any], bool]`	Receives the state and returns a `bool`; any other value raises `GraphExecutionError` at run time.
`target`	`Node \| EndSentinel`	Target when the predicate is true.
`otherwise`	`Node \| EndSentinel`	Target when the predicate is false.

Raises
`TypeError`	If `predicate` is not callable.

FlowBranch(router, mapping, router_ref=None, requires_bool=False)

Conditional routing table produced by branch or when.

Attributes
`router`	`Callable[[Any], Any]`	Called with the state; its result picks the target in `mapping`.
`mapping`	`Mapping[Any, Node \| EndSentinel]`	Router result to the next node or `END`.
`router_ref`	`str \| None`	`module:qualname` import path of the router, for `Graph.to_spec`.
`requires_bool`	`bool`	The router must return a `bool`; set by `when`.