Checkpoints unable to write to local disk

Description

A clear description of the bug

LocalResultHandler isn’t able to write to the folder that’s created when checkpoint=True.

I’m just guessing that prefect’s creating the temporary directory with the intention of saving the serialized object there. But it seems that perhaps it’s trying to write the serialized object before the temporary directory is created? Not sure!

Expected Behavior

What did you expect to happen instead?

https://docs.prefect.io/core/concepts/persistence.html#checkpointing

Reproduction

A minimal example that exhibits the behavior.

test_cache.py:

from prefect import task, Flow
from prefect.engine.result_handlers import LocalResultHandler

@task(checkpoint=True, result_handler=LocalResultHandler(dir="~/.prefect"))
def hello():
    return 'hello'

with Flow('test checkpoint') as flow:
    h = hello()

flow.run()

$ python test_cache.py 
[2020-01-07 20:20:30,905] INFO - prefect.FlowRunner | Beginning Flow run for 'test checkpoint'
[2020-01-07 20:20:30,908] INFO - prefect.FlowRunner | Starting flow run.
[2020-01-07 20:20:30,916] INFO - prefect.TaskRunner | Task 'print_df': Starting task run...
[2020-01-07 20:20:30,917] ERROR - prefect.TaskRunner | Unexpected error: FileNotFoundError(2, 'No such file or directory')
Traceback (most recent call last):
  File "/Users/bryanwhiting/venvs/py37/lib/python3.7/site-packages/prefect/engine/runner.py", line 48, in inner
    new_state = method(self, state, *args, **kwargs)
  File "/Users/bryanwhiting/venvs/py37/lib/python3.7/site-packages/prefect/engine/task_runner.py", line 907, in get_task_run_state
    state._result.store_safe_value()
  File "/Users/bryanwhiting/venvs/py37/lib/python3.7/site-packages/prefect/engine/result.py", line 90, in store_safe_value
    value = self.result_handler.write(self.value)
  File "/Users/bryanwhiting/venvs/py37/lib/python3.7/site-packages/prefect/engine/result_handlers/local_result_handler.py", line 58, in write
    fd, loc = tempfile.mkstemp(prefix="prefect-", dir=self.dir)
  File "/usr/local/Cellar/python/3.7.5/Frameworks/Python.framework/Versions/3.7/lib/python3.7/tempfile.py", line 340, in mkstemp
    return _mkstemp_inner(dir, prefix, suffix, flags, output_type)
  File "/usr/local/Cellar/python/3.7.5/Frameworks/Python.framework/Versions/3.7/lib/python3.7/tempfile.py", line 258, in _mkstemp_inner
    fd = _os.open(file, flags, 0o600)
FileNotFoundError: [Errno 2] No such file or directory: '~/.prefect/prefect-bdz439pq'
[2020-01-07 20:20:30,946] INFO - prefect.TaskRunner | Task 'print_df': finished task run for task with final state: 'Failed'
[2020-01-07 20:20:30,947] INFO - prefect.FlowRunner | Flow run FAILED: some reference tasks failed.

Environment

Any additional information about your environment

• Python 3.7.5
• prefect 0.8.1

I’m loving the new releases of Prefect! You guys are definitely heading in the right direction. Keep it up!!!

[bryanwhiting]

Fascinating!! Thanks for the reply. I’m super excited to see what the checkpointing solution looks like. That’s going to be a definite game changer/airflow killer! Great work and thanks for the detailed response.

[cicdw]

Hi @mivade - yea we’re aiming to release the new Results API later next week (in 0.11.0) which will include a more user friendly caching mechanism. You’re more than welcome to open an issue in the meantime, but I’ll be most curious to hear whether the new API satisfies your use case or not so it might be worthwhile to hold off until it’s released!