question about for-loops on mappings

i am trying to get a for loop over a dict (not a list)

is there some best-practice function that would e.g. unfold dict.keys() to a visitable list ?

```
snapcraft.yaml.template:24:10:
  'Expression' object has no attribute 'visited':
   $_.epackages[$_.version][$_.name].keys()
Finished with errors.
```

thanks in advance