Errors raised when executing an Ewoks task

Warning

To showcase the errors raised when executing a task, we use the task execution mechanism described in Execute a task from Python.

Be sure to read Execute a task from Python before reading this page.

The principle stays the same when executing a task in a workflow.

An exception encountered when running an Ewoks task will always be chained with a RuntimeError telling which task failed:

>>> from ewokscore.tests.examples.tasks.sumtask import SumTask
>>> task = SumTask(inputs={"a": 'a_string', "b": 10})
>>> task.execute()
Traceback (most recent call last):
  <...>
TypeError: can only concatenate str (not "int") to str

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  <...>
RuntimeError: Task 'ewokscore.tests.examples.tasks.sumtask.SumTask' failed

The top-level exception will always be RuntimeError while the real exception (in this case TypeError) is one level below.

This is particularly important when testing or catching exceptions:

>>> task = SumTask(inputs={"a": 'a_string', "b": 10})
>>> try:
...    task.execute()
... except TypeError as e:
...     print('TYPE_ERROR')
...     exception = e
... except RuntimeError as e:
...     print('RUNTIME_ERROR')
...     exception = e
RUNTIME_ERROR
>>> exception
RuntimeError("Task 'ewokscore.tests.examples.tasks.sumtask.SumTask' failed")

We see here that the error caught is indeed the RuntimeError and not the TypeError. To retrieve the original error, we have to go back to the RuntimeError cause:

>>> original_exception = exception.__cause__
>>> original_exception
TypeError('can only concatenate str (not "int") to str')

Full code

from ewokscore.tests.examples.tasks.sumtask import SumTask

task = SumTask(inputs={"a": 'a_string', "b": 10})
try:
   task.execute()
except TypeError as e:
    print('TYPE_ERROR')
    exception = e
except RuntimeError as e:
    print('RUNTIME_ERROR')
    exception = e
original_exception = exception.__cause__