Intro: Fault-Oblivious Stateful Python Code

cadence-python allows you to create Python functions that have their state (local variables etc..) implicitly saved such that if the process/machine fails the state of the function is not lost and can resume from where it left off.

This programming model is useful whenever you need to ensure that a function runs to completion. For example:

• Business logic involving multiple micro services
• CI/CD pipelines
• Data pipelines
• RPA
• ETL
• Marketing automation / Customer journeys / Customer engagement
• Zapier/IFTTT like end user automation.
• Chat bots
• Multi-step forms
• Scheduler/Cron jobs

Behind the scenes, cadence-python uses Cadence as its backend.

For more information about the fault-oblivious programming model refer to the Cadence documentation here

Install Cadencce

wget https://raw.githubusercontent.com/uber/cadence/master/docker/docker-compose.yml
docker-compose up

Register sample domain

docker run --network=host --rm ubercadence/cli:master --do sample domain register -rd 1

Installation cadence-python

pip install cadence-client==1.0.1

Hello World Sample

importsysimportloggingfromcadence.activity_methodimportactivity_methodfromcadence.workerfactoryimportWorkerFactoryfromcadence.workflowimportworkflow_method, Workflow, WorkflowClientlogging.basicConfig(level=logging.DEBUG)
TASK_LIST="HelloActivity-python-tasklist"DOMAIN="sample"# Activities InterfaceclassGreetingActivities:
@activity_method(task_list=TASK_LIST, schedule_to_close_timeout_seconds=2)defcompose_greeting(self, greeting: str, name: str) ->str:
raiseNotImplementedError# Activities ImplementationclassGreetingActivitiesImpl:
defcompose_greeting(self, greeting: str, name: str):
returnf"{greeting}{name}!"# Workflow InterfaceclassGreetingWorkflow:
@workflow_method(execution_start_to_close_timeout_seconds=10, task_list=TASK_LIST)asyncdefget_greeting(self, name: str) ->str:
raiseNotImplementedError# Workflow ImplementationclassGreetingWorkflowImpl(GreetingWorkflow):
def__init__(self):
self.greeting_activities: GreetingActivities=Workflow.new_activity_stub(GreetingActivities)
asyncdefget_greeting(self, name):
# Place any Python code here that you want to ensure is executed to completion.# Note: code in workflow functions must be deterministic so that the same code paths# are ran during replay.returnawaitself.greeting_activities.compose_greeting("Hello", name)
if__name__=='__main__':
factory=WorkerFactory("localhost", 7933, DOMAIN)
worker=factory.new_worker(TASK_LIST)
worker.register_activities_implementation(GreetingActivitiesImpl(), "GreetingActivities")
worker.register_workflow_implementation_type(GreetingWorkflowImpl)
factory.start()
client=WorkflowClient.new_client(domain=DOMAIN)
greeting_workflow: GreetingWorkflow=client.new_workflow_stub(GreetingWorkflow)
result=greeting_workflow.get_greeting("Python")
print(result)
print("Stopping workers....")
worker.stop()
print("Workers stopped...")
sys.exit(0)

Status / TODO

cadence-python is still under going heavy development. It should be considered EXPERIMENTAL at the moment. A production version is targeted to be released in September of 2019January 2020March 2020 April 2020.

1.0

• Tchannel implementation
• Python-friendly wrapper around Cadence's Thrift API
• Author activities in Python
• Start workflows (synchronously)
• Create workflows
• Workflow execution in coroutines
• Invoke activities from workflows
• ActivityCompletionClient heartbeat, complete, complete_exceptionally
• Activity heartbeat, getHeartbeatDetails and doNotCompleteOnReturn
• Activity retry
• Activity getDomain(), getTaskToken(), getWorkflowExecution()
• Signals
• Queries
• Async workflow execution
• await
• now (currentTimeMillis)
• Sleep
• Loggers
• newRandom
• UUID
• Workflow Versioning
• WorkflowClient.newWorkflowStub(Class workflowInterface, String workflowId);

1.1

• ActivityStub and Workflow.newUntypedActivityStub
• Classes as arguments and return values to/from activity and workflow methods
• WorkflowStub and WorkflowClient.newUntypedWorkflowStub
• Custom workflow ids through start() and new_workflow_stub()
• ContinueAsNew
• Compatibility with Java client
• Compatibility with Golang client

2.0

• Sticky workflows

Post 2.0:

• sideEffect/mutableSideEffect
• Local activity
• Parallel activity execution
• Timers
• Cancellation Scopes
• Child Workflows
• Explicit activity ids for activity invocations