We need to create validators for each status. The validator will check if transition from current state is allowed or not. WorkflowExecutionValidator will pick up an appropriate validator from a list and check if transition is allowed. Validators are implemented for each workflow execution status Validators are applied in production code

class WorkflowExecutionValidator(object):
    def __init__(self, workflow_execution: WorkflowExecution):
        self.workflow_execution = workflow_execution

    def validate(self):
        validators = [
            InitialValidator(),
            ProcessingValidator(),
            FailedValidator(),
            CompletedValidator()
        ]

        for validator in validators:
            if validator.is_validator_for(self.workflow_execution):
                return validator.validate(self.workflow_execution)