How should one get an op's output and concatenate it with another op's output?

[ivanov-slk]

I'm using dagster==0.13.19 on Linux and Python 3.9.

How should I take an op's output and concatenate it with another op's output? Let's suppose that both ops output lists.

Example code:

### zzz.py
from dagster import op, job

@op
def op_a(context):
    return [1,2,3]

@op
def op_b(context):
    return [4,5,6]

@job
def job_a():
    print(type(op_a))
    a = op_a()
    print(type(a))
    b = op_b()
    print(a+b)

When I execute this with python zzz.py I get the following error:

<class 'dagster.core.definitions.op_definition.OpDefinition'>
<class 'dagster.core.definitions.composition.InvokedSolidOutputHandle'>
Traceback (most recent call last):
  File "/home/myself/zzz.py", line 12, in <module>
    def job_a():
  File "/home/myself/.venv/lib/python3.9/site-packages/dagster/core/definitions/decorators/job.py", line 186, in job
    return _Job()(name)
  File "/home/myself/.venv/lib/python3.9/site-packages/dagster/core/definitions/decorators/job.py", line 63, in __call__
    ) = do_composition(
  File "/home/myself/.venv/lib/python3.9/site-packages/dagster/core/definitions/composition.py", line 1008, in do_composition
    output = fn(**kwargs)
  File "/home/myself/zzz.py", line 17, in job_a
    print(a+b)
TypeError: unsupported operand type(s) for +: 'InvokedSolidOutputHandle' and 'InvokedSolidOutputHandle'

I can see that ops return InvokedSolidOutputHandle. Is this okay? I thought that solids were deprecated some time ago and one should be able to get the op's output directly and use it in, e.g., addition etc.

In case this is desired, how should I concatenate these two lists?

Thank you!

[alangenfeld]

The @job decorated function runs only at initialization time to build the dependency structure. If you want to do any computation on data, it has to happen in an @op.

https://docs.dagster.io/concepts/ops-jobs-graphs/jobs-graphs#fixed-fan-in may be relevant if your end goal is beyond just concatenating the outputs.

[ivanov-slk]

A classic example of the XY problem on my side :D
I was indeed trying to put these two ops' outputs into a third op.

Anyway, thanks for guessing my real problem and the documentation link :)