remove redundant tuple conversions

bilby/core/prior/dict.py

@@ -380,8 +380,8 @@ class PriorDict(dict):
             return all_samples
 
     def normalize_constraint_factor(self, keys):
-        if tuple(keys) in self._cached_normalizations.keys():
-            return self._cached_normalizations[tuple(keys)]
+        if keys in self._cached_normalizations.keys():
+            return self._cached_normalizations[keys]
         else:
             min_accept = 1000
             sampling_chunk = 5000
@@ -398,7 +398,7 @@ class PriorDict(dict):
                         [all_samples[key], samples[key].flatten()])
                 keep = np.array(self.evaluate_constraints(all_samples), dtype=bool)
             factor = len(keep) / np.count_nonzero(keep)
-            self._cached_normalizations[tuple(keys)] = factor
+            self._cached_normalizations[keys] = factor
             return factor
 
     def prob(self, sample, **kwargs):