Check for pickled graph first, return empty nodes and edges for edge-…

…case

mira/dkg/construct.py

@@ -456,12 +456,12 @@ def extract_ontology_subtree(curie: str, add_subtree: bool = False):
  if resource_prefix == "ncbitaxon":
  type = "class"
  version=get_version(resource_prefix)
- _, obo_path = _ensure_ontology_path(resource_prefix,force=False,
- version=version)
  cached_relabeled_obo_graph_path = prefix_directory_join(resource_prefix,
  name="relabeled_obo_graph.pkl",
  version=version)
  if not cached_relabeled_obo_graph_path.exists():
+ _, obo_path = _ensure_ontology_path(resource_prefix, force=False,
+ version=version)
  obo_graph = read_obo(obo_path)
  relabeled_graph = networkx.relabel_nodes(obo_graph,
  lambda node_index: node_index.lower())
@@ -472,6 +472,8 @@ def extract_ontology_subtree(curie: str, add_subtree: bool = False):
  relabeled_graph_file = open(cached_relabeled_obo_graph_path, 'rb')
  relabeled_graph = pickle.load(relabeled_graph_file)
  relabeled_graph_file.close()
+ else:
+ return nodes, edges
 
  node = relabeled_graph.nodes.get(curie)
  if not node: