Move cache type check outside of decorated method

Define function for returning the method cache dict outside of the wrapped method so it doesn't need to be checked every method call.

Author: chriseclectic

qiskit_experiments/framework/cache_method.py

@@ -46,23 +46,35 @@ def cache_method_decorator(method: Callable) -> Callable:
         Returns:
             The wrapped cached method.
         """
+        # Function for returning cache key
         cache_key_fn = _cache_key_function(cache_args, require_hashable)
 
-        @functools.wraps(method)
-        def _cached_method(self, *args, **kwargs):
-            # Initialize cache if none provided
-            if isinstance(cache, str):
+        # Function for returning cache dict
+        if isinstance(cache, str):
+
+            def _cache_fn(self, method):
                 if not hasattr(self, cache):
                     setattr(self, cache, {})
                 instance_cache = getattr(self, cache)
-            else:
-                instance_cache = cache
+                name = method.__name__
+                if name not in instance_cache:
+                    instance_cache[name] = {}
+                return instance_cache[name]
+
+        else:
 
-            name = method.__name__
-            if name not in instance_cache:
-                instance_cache[name] = {}
-            meth_cache = instance_cache[name]
+            def _cache_fn(self, method):
+                # pylint: disable = unused-argument
+                name = method.__name__
+                if name not in cache:
+                    cache[name] = {}
+                return cache[name]
 
+        # Cached method function
+
+        @functools.wraps(method)
+        def _cached_method(self, *args, **kwargs):
+            meth_cache = _cache_fn(self, method)
             key = cache_key_fn(*args, **kwargs)
             if key in meth_cache:
                 return meth_cache[key]