add ws function to check if a PDB entry exists

Former-commit-id: 6d985f2167bda81cb08bad3b9cc5e4738a96e5a1

ippisite/ippidb/ws.py

@@ -83,3 +83,12 @@ def get_pdb_uniprot_mapping(pdb_id):
     resp = requests.get('https://www.ebi.ac.uk/pdbe/api/mappings/uniprot/{}'.format(pdb_id.lower()))
     uniprot_ids = list(resp.json()[pdb_id]['UniProt'].keys())
     return uniprot_ids
+
+def pdb_entry_exists(pdb_id):
+    """ test if a PDB entry exists using EBI web services """
+    resp = requests.get('https://www.ebi.ac.uk/pdbe/api/pdb/entry/summary/{}'.format(pdb_id.lower()))
+    # EBI sends back either a 404 or an empty json if the PDB does not exist
+    if not(resp.ok):
+        return False
+    else:
+        return True