[BUG] Edge case for the unpack_to argument

[matthiasmindee]

from tawazi import xn

@xn(unpack_to=1)
def toto():
    ...

this leads to unexpected behaviours

[bashirmindee]

what is the expected behavior and what is happening ?

[matthiasmindee]

this makes the execution freeze. The expected behaviour would either be to trigger an exception saying that there's nothing to unpack, or not try to unpack the result

[bashirmindee]

from tawazi import xn, dag

@xn(unpack_to=1)
def toto():
    ...

@dag
def pipe():
    return toto()

pipe()

This doesn't hang locally

[bashirmindee]

I am getting this:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/bashir/mindee/tawazi/tawazi/_dag/dag.py", line 674, in __call__
    return self._get_return_values(all_nodes_dict)  # type: ignore[return-value]
  File "/home/bashir/mindee/tawazi/tawazi/_dag/dag.py", line 736, in _get_return_values
    return tuple(gen)
  File "/home/bashir/mindee/tawazi/tawazi/_dag/dag.py", line 734, in <genexpr>
    gen = (ren_uxn.result(xn_dict) for ren_uxn in return_uxns)
  File "/home/bashir/mindee/tawazi/tawazi/node/node.py", line 639, in result
    return _filter_noval(reduce(lambda obj, key: obj.__getitem__(key), self.key, xn.result))
  File "/home/bashir/mindee/tawazi/tawazi/node/node.py", line 639, in <lambda>
    return _filter_noval(reduce(lambda obj, key: obj.__getitem__(key), self.key, xn.result))
AttributeError: 'NoneType' object has no attribute '__getitem__'

[matthiasmindee]

well that's weird

[bashirmindee]

yes but it doesn't hang... The problem here is that pass means that the function doesn't return a Tuple... It returns None! This is why we have this error. For Example if you write this, the code works as expected:

from tawazi import xn, dag

@xn(unpack_to=1)
def toto():
    return (1,)

@dag
def pipe():
    v, = toto()
    return v

assert 1 == pipe()

[bashirmindee]

what action do you think should be taken ?

[matthiasmindee]

yes but

@xn(unpack_to=1)
def toto():
    return 1

fails

I think we should actually ban unpack_to=1 since this is most probably unwanted by the user

[bashirmindee]

of course it fails because 1 is not a tuple...

[matthiasmindee]

yes that exactly my point ahahah

[bashirmindee]

Python allows for single valued Tuples... This is why it is supported. I agree that I don't see the point of having a tuple which contains a single value but this is Python XD

[matthiasmindee]

yeah I'd suggest banning that altogether since it's error-prone anyways

[bashirmindee]

I think we should have at least a clearer error message. Because even if we replace unpack_to=1 by unpack_to=2 we get the same error message. So I believe the problem lies in the error message more than in the unpack_to=1...

[bashirmindee]

stale