Create pubchem_ext.py

mcp/pubchem_ext.py

@@ -0,0 +1,46 @@
+"""
+pubchem_ext.py  ·  PubChem PUG-REST helper
+Docs: https://pubchem.ncbi.nlm.nih.gov/docs/pug-rest-tutorial  📄
+
+• No API-key is required for the public endpoint.
+• If you set PUBCHEM_KEY (token), we include it as X-Pubchem-ApiKey
+  which lifts burst limits.  Otherwise header is omitted.
+• One retry on 5xx / ReadTimeout, then returns {}.
+"""
+
+from __future__ import annotations
+import os, asyncio, httpx
+from urllib.parse import quote_plus
+from functools import lru_cache
+from typing import Dict
+
+_TOKEN = os.getenv("PUBCHEM_KEY")           # optional
+_BASE  = "https://pubchem.ncbi.nlm.nih.gov/rest/pug"
+_HDR   = {"Accept": "application/json"}
+if _TOKEN:
+    _HDR["X-Pubchem-ApiKey"] = _TOKEN
+
+@lru_cache(maxsize=256)
+async def fetch_compound(name: str) -> Dict:
+    """
+    Return compound data as dict or {} on failure.
+    Uses /compound/name/<drug>/JSON endpoint.
+    """
+    url = f"{_BASE}/compound/name/{quote_plus(name)}/JSON"
+
+    async def _hit() -> Dict:
+        async with httpx.AsyncClient(timeout=10, headers=_HDR) as cli:
+            r = await cli.get(url)
+            if r.status_code == 404:
+                return {}                 # no such compound
+            r.raise_for_status()
+            return r.json()
+
+    try:
+        return await _hit()
+    except (httpx.HTTPStatusError, httpx.ReadTimeout):
+        await asyncio.sleep(0.5)          # quick back-off
+        try:
+            return await _hit()
+        except Exception:
+            return {}                     # graceful fallback