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Python DSLAPI: Streams
Python API reference join | multi_join | merge | split | case | cycle_link | error | when

Join, Merge, Split, Case, and control streams

Multi-input, branching, cycle, condition, and error-flow operators.

When to use

Use these methods where graph shape, state retention, or control flow is the primary behavior.

Behavior

  • Join combines exactly two KeyValue flows. MultiJoin combines one primary and one or more ordered additional KeyValue flows.
  • Merge combines sources without a user callback.
  • Split broadcasts; Case selects exactly one zero-based When branch.
  • CycleLink closes an intentional graph cycle; Error receives failure flow.

Join methods properties

Stateful combination.

PropertyTypeDescription
join(..., function, join_type=None, join_storage=None)Stream

Two-input keyed join. Set JoinType.INNER, LEFT, RIGHT, or OUTER and JoinStorageType.HASH_MAP before validation.

multi_join(..., function, join_storage=None)Stream

Variable-input keyed join with one primary source and at least one ordered additional source. Set JoinStorageType.HASH_MAP before validation.

source / sourcesStream | Sequence[Stream]

source is callback slot 0. sources are slot 1 for Join and ordered slots 1..N for MultiJoin.

ttl / renew_ttlint | bool | None

Retention in milliseconds and renewal after an arrival when the callback returns false.

join callback resultbool

True completes the key and clears retained values; False waits for later arrivals.

Routing methods properties

Graph branching and recombination.

PropertyTypeDescription
merge(name, *, sources=(), appearance=None)Stream

Combine multiple sources.

split(name, *, source=None, appearance=None)Stream

Create a branch point.

case(name, *, function, source=None, appearance=None)Stream

Build a selector that returns the zero-based index of exactly one attached When branch.

when(name, *, value_type=None, source=None, appearance=None)Stream

Register an ordered, typed branch on a Case. When has no Function of its own.

Control methods properties

Cycles and failures.

PropertyTypeDescription
cycle_link(name, *, source=None, appearance=None)Stream

Explicit cycle connector.

error(name, *, value_type=None, function=None, source=None, appearance=None)Stream

Failure stream with optional callback.

Python example

merged = orders.merge("Merge Results")
merged << http_result << kafka_result << processing_error

split = orders.split("Split Result")
merged >> split
split >> success
split >> retry