Dump and restore not working properly / strange KeyError

[sschlueters]

I stumbled upon a strange error. The EnergySystem.flows method doesn't work, when the energy system was dumped and restored. Here is a minimal example:

from oemof.solph import EnergySystem, Bus, Flow, Source

es_orig = EnergySystem()

bus = Bus(label="electricity")
source = Source(label="grid", outputs={bus: Flow(variable_costs=1)})

es_orig.add(bus, source)

print(es_orig.flows())

print("Now we dump and restore...")
es_orig.dump(dpath='.', filename='test.oemof')

es_restored = EnergySystem()
es_restored.restore(dpath='.', filename='test.oemof')

print(es_restored.flows())

I get as an output:

{("<oemof.solph.network.Source: 'grid'>", "<oemof.solph.network.Bus: 'electricity'>"): '<oemof.solph.network.Flow: EdgeLabel(input="<oemof.solph.network.Source: \'grid\'>", output="<oemof.solph.network.Bus: \'electricity\'>")>'}
Now we dump and restore...
Traceback (most recent call last):
  File ".\debug.py", line 25, in <module>
    print(es_restored.flows())
  File "D:\bin\anaconda3\envs\oemof\lib\site-packages\oemof\network\energy_system.py", line 179, in flows
    for source in self.nodes
  File "D:\bin\anaconda3\envs\oemof\lib\site-packages\oemof\network\energy_system.py", line 180, in <dictcomp>
    for target in source.outputs
  File "D:\bin\anaconda3\envs\oemof\lib\collections\__init__.py", line 1027, in __getitem__
    raise KeyError(key)
KeyError: "<oemof.solph.network.Bus: 'electricity'>"

Even

grid_node, = [node for node in es_restored.nodes if node.label == 'grid']
key, = [k for k in grid_node.outputs.keys()]
print(grid_node.outputs[key])

fails after dumping and restoring the energy system.

[sschlueters]

I don't know how to solve this issue, but @jnnr seemed to have similar intentions while discovering this bug: analysis of the oemof results. In the end I worked my way around this problem and wrote some functions which work for me. Maybe they are useful for others: https://gist.github.com/sschlueters/4af0f5f035ea3f38f6050e818aba776c

Edit: The functions expect the results as given by results = oemof.solph.processing.results(model)

[jnnr]

I could fix the KeyError by replacing

(source, target): source.outputs[target]

with

(source, target): source.outputs.get(target)

in the flows() method, which is said to be a usual solution in case of KeyErrors. Still not 100% sure why this works.

[jnnr]

I could fix the KeyError by replacing

Ok, that was trivial - too quick. .get returns None if the key is not found, so this is not really a fix.

[jnnr]

The funny thing is that the key seems to be present. I checked and found that the hash is correct.

[jnnr]

I made some further observations in oemof/oemof-solph#742 (comment), but I am stuck again. Any ideas, @oemof/oemof-core?

[p-snft]

I found a related issue. I think it's because Nodes have a hash function that is depending on the label. The label, however, seems always set (in time) when restoring a model.

https://github.com/oemof/oemof-network/pull/43/files#diff-7cfcaf50c32fb4054e7474030d8097d8987c25da20fcc93b00c32c591a087ac4R81