Cache SO names (#199)

A lot of resources (HGNC, PomBase, ZFIN) require SO names for
legibility, so this caches them

src/pyobo/resources/so.py

@@ -0,0 +1,55 @@
+"""Loading of the relations ontology names."""
+
+from __future__ import annotations
+
+import csv
+import os
+from functools import lru_cache
+
+import requests
+
+__all__ = [
+    "get_so_name",
+    "load_so",
+]
+
+HERE = os.path.abspath(os.path.dirname(__file__))
+SO_PATH = os.path.join(HERE, "so.tsv")
+SO_JSON_URL = "https://github.com/The-Sequence-Ontology/SO-Ontologies/raw/refs/heads/master/Ontology_Files/so-simple.json"
+SO_URI_PREFIX = "http://purl.obolibrary.org/obo/SO_"
+
+
+def get_so_name(so_id: str) -> str | None:
+    """Get the name from the identifier."""
+    return load_so().get(so_id)
+
+
+@lru_cache(maxsize=1)
+def load_so() -> dict[str, str]:
+    """Load the Sequence Ontology names."""
+    if not os.path.exists(SO_PATH):
+        download_so()
+    with open(SO_PATH) as file:
+        return dict(csv.reader(file, delimiter="\t"))
+
+
+def download_so():
+    """Download the latest version of the Relation Ontology."""
+    rows = []
+    res_json = requests.get(SO_JSON_URL).json()
+    for node in res_json["graphs"][0]["nodes"]:
+        uri = node["id"]
+        if not uri.startswith(SO_URI_PREFIX):
+            continue
+        identifier = uri.removeprefix(SO_URI_PREFIX)
+        name = node.get("lbl")
+        if name:
+            rows.append((identifier, name))
+
+    with open(SO_PATH, "w") as file:
+        writer = csv.writer(file, delimiter="\t")
+        writer.writerows(sorted(rows, key=lambda x: int(x[0])))
+
+
+if __name__ == "__main__":
+    download_so()