Enable caching for get_ion_reference_data (#429)

src/mp_api/client.py

@@ -2,7 +2,7 @@
 import warnings
 from functools import lru_cache
 from os import environ
-from typing import List, Optional, Tuple, Union
+from typing import List, Optional, Tuple, Union, Dict
 from typing_extensions import Literal
 
 from emmet.core.mpid import MPID
@@ -533,10 +533,7 @@ def get_pourbaix_entries(
 
         return pbx_entries
 
-    # TODO - @lru_cache causes this method to fail when chemsys is given as a list,
-    # with an 'unhashable type' error
-    # @lru_cache
-    def get_ion_reference_data(self, chemsys: Union[str, List]) -> List[dict]:
+    def get_ion_reference_data(self, chemsys: Union[str, List]) -> List[Dict]:
         """
         Download aqueous ion reference data used in the construction of Pourbaix diagrams.
 
@@ -575,7 +572,14 @@ def get_ion_reference_data(self, chemsys: Union[str, List]) -> List[dict]:
         # capitalize and sort the elements
         chemsys = sorted(e.capitalize() for e in chemsys)
 
-        # TODO - see if there is a way to avoid querying the entire collection
+        # convert to a tuple which is hashable
+        return self._get_ion_reference_data(tuple(chemsys))  # type: ignore
+
+    @lru_cache  # type: ignore
+    def _get_ion_reference_data(self, chemsys: Tuple):  # type: ignore
+        """
+        Private, cacheable helper method for get_ion_reference data.
+        """
         ion_data = [
             d
             for d in self.contribs.contributions.get_entries(

src/mp_api/core/client.py

@@ -368,7 +368,7 @@ def get_data_by_id(
 
         try:
             results = self._query_resource_data(
-                criteria=criteria, fields=fields, suburl=document_id,
+                criteria=criteria, fields=fields, suburl=document_id,  # type: ignore
             )
         except MPRestError:
 
@@ -388,7 +388,7 @@ def get_data_by_id(
                     document_id = new_document_id
 
                     results = self._query_resource_data(
-                        criteria=criteria, fields=fields, suburl=document_id,
+                        criteria=criteria, fields=fields, suburl=document_id,  # type: ignore
                     )
 
         if not results: