python 3.7 syntax, not 3.9+ for functools caching

Author: JacksonBurns

rmgpy/yml.py

@@ -34,7 +34,7 @@
 
 import os
 import yaml
-from functools import cache
+from functools import lru_cache
 
 from rmgpy.chemkin import load_chemkin_file
 from rmgpy.species import Species
@@ -105,7 +105,7 @@ def get_radicals(spc):
     else:
         return spc.molecule[0].multiplicity-1
 
-@cache
+@lru_cache(maxsize=None)
 def obj_to_dict(obj, spcs, names=None, label="solvent"):
     result_dict = dict()
     if isinstance(obj, Species):