changed from repr to tuple to convert list to something that can be used as a...

changed from repr to tuple to convert list to something that can be used as a dict key, and make cached attribute 'protected' with _

bilby/core/prior/dict.py

@@ -41,7 +41,7 @@ class PriorDict(dict):
             self.from_file(filename)
         elif dictionary is not None:
             raise ValueError("PriorDict input dictionary not understood")
-        self.cached_normalizations= {}
+        self._cached_normalizations= {}
 
         self.convert_floats_to_delta_functions()
 
@@ -380,8 +380,8 @@ class PriorDict(dict):
             return all_samples
 
     def normalize_constraint_factor(self, keys):
-        if repr(keys) in self.cached_norm_factors.keys():
-            return self._cached_normalizations[repr(keys)]
+        if tuple(keys) in self._cached_normalizations.keys():
+            return self._cached_normalizations[tuple(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[repr(keys)] = factor
+            self._cached_normalizations[tuple(keys)] = factor
             return factor
 
     def prob(self, sample, **kwargs):