How to define a Signal in Python

To define a Signal, set the Signal decorator @workflow.signal on the Signal function inside your Workflow.

@workflow.signal
def your_signal(self, value: str) -> None:
    self._signal = value

The @workflow.signal decorator defines a method as a Signal. Signals can be asynchronous or synchronous methods and can be inherited; however, if a method is overridden, the override must also be decorated.

Dynamic Signals

You can use @workflow.signal(dynamic=True), which means all other unhandled Signals fall through to this.

Your method parameters must be self, a string signal name, and a *args variable argument parameter.

For example:

@workflow.signal(dynamic=True)
def signal_dynamic(self, name: str, *args: Any) -> None:
    self._last_event = f"signal_dynamic {name}: {args[0]}"

Customize name

Non-dynamic methods can only have positional arguments. Temporal suggests taking a single argument that is an object or data class of fields that can be added to as needed.

Return values from Signal methods are ignored.

You can have a name parameter to customize the Signal's name, otherwise it defaults to the unqualified method __name__.

The following example sets a custom Signal name.

@workflow.signal(name="Custom-Name")
def signal(self, arg: str) -> None:
    self._last_event = f"signal: {arg}"

note

You can either set the name or the dynamic parameter in a Signal's decorator, but not both.