Fix thread safety bug in lazy load pattern

Author: musicsnobj

zxcvbn/matching.py

@@ -22,10 +22,9 @@ def get_ranked_dictionaries():
         # Do the expensive import here only
         from zxcvbn.frequency_lists import FREQUENCY_LISTS
 
-        # Build the dictionary once
-        RANKED_DICTIONARIES = {}
-        for name, lst in FREQUENCY_LISTS.items():
-          RANKED_DICTIONARIES[name] = build_ranked_dict(lst)
+        # Build in local scope before adding to global scope for thread safety
+        built_dict = {name: build_ranked_dict(lst) for name, lst in FREQUENCY_LISTS.items()}
+        RANKED_DICTIONARIES = built_dict
     return RANKED_DICTIONARIES
 
 
@@ -40,6 +39,7 @@ def wrapper(*args, **kwargs):
         return func(*args, **kwargs)
     return wrapper
 
+
 GRAPHS = {
     'qwerty': adjacency_graphs.ADJACENCY_GRAPHS['qwerty'],
     'dvorak': adjacency_graphs.ADJACENCY_GRAPHS['dvorak'],