Repair function for a nested database

[Alfalfa]

I made a class handle the preference database of my apps. The problem is that as new features are added, using the get() method on the new keys raise KeyErrors. To make this foolproof, I would like to add a repair() method, which would be called on init if the keys of the current database does not match the default keys. I was wondering if there would be an easy way to do that, and that would be reliable with various nesting levels.

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#!/usr/bin/python3 import json import os   LOCAL_DIR = os.path.dirname(os.path.realpath(__file__)) + '/' PREFERENCES_FILE = LOCAL_DIR + "preferences.json"   PREFERENCES_DEFAULT = \ {     'Key A':     {         'sub key':         {             'value': 0,         }     },     'Key B':     {         'value': 1     },     'Key C': 2, }   PREFERENCES_BROKEN = \ {     'Key A':     {         'sub key':         {         }     },     'Key B':     {     }, }     def copyDict(dictionnary):     # from https://writeonly.wordpress.com/2009/05/07/deepcopy-is-a-pig-for-simple-data     out = dict().fromkeys(dictionnary)     for key, value in dictionnary.items():         try:             out[key] = value.copy()  # dicts, sets         except AttributeError:             try:                 out[key] = value[:]  # lists, tuples, strings, unicode             except TypeError:                 out[key] = value  # ints     return out     class Database():     def __init__(self):         if os.path.isfile(PREFERENCES_FILE) and os.stat(PREFERENCES_FILE).st_size > 0:             self.load()             if not self.verify():                 self.repair()         else:             self.db = copyDict(PREFERENCES_DEFAULT)             with open(PREFERENCES_FILE, "w") as f:                 f.write(json.dumps(self.db, indent=2, sort_keys=False))             print("Created preferences file")       def get(self, *keys, db=None):         if not db: db = self.db         for key in keys:             db = db[key]         return db       def load(self):         with open(PREFERENCES_FILE, "r") as f:             self.db = json.load(f)         print("Loaded preferences database")       def repair(self):         #self.save()         pass       def save(self):         with open(PREFERENCES_FILE, "w") as f:             f.write(json.dumps(self.db, indent=2, sort_keys=False))         print("Saved preferences database")       def verify(self):         db = [x for x in self.walk(self.db)]         default = [x for x in self.walk(PREFERENCES_DEFAULT)]         return db == default       def walk(self, indict, pre=None):         # From https://stackoverflow.com/a/12507546         pre = pre[:] if pre else []         if isinstance(indict, dict):             for key, value in indict.items():                 if isinstance(value, dict):                     for d in self.walk(value, [key] + pre):                         yield d                 elif isinstance(value, list) or isinstance(value, tuple):                     for v in value:                         for d in self.walk(v, [key] + pre):                             yield d                 else:                     yield pre + [key]         else:             yield indict     # Working database example if os.path.isfile(PREFERENCES_FILE):     os.remove(PREFERENCES_FILE)   db = Database() print("# GOOD DATABASE") print(db.get("Key A", "sub key", "value")) print(db.get("Key B", "value")) print(db.get("Key C")) print()   # Broken database example with open(PREFERENCES_FILE, "w") as f:     f.write(json.dumps(PREFERENCES_BROKEN, indent=2, sort_keys=False))   db = Database() print("# BROKEN DATABASE") print(db.get("Key A", "sub key", "value")) print(db.get("Key B", "value")) print(db.get("Key C"))

[Alfalfa]

I solved it with a recursive function and setdefault()

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class Database():     def __init__(self):         if os.path.isfile(PREFERENCES_FILE) and os.stat(PREFERENCES_FILE).st_size > 0:             self.load()             self.validate()         else:             self.db = copyDict(PREFERENCES_DEFAULT)             with open(PREFERENCES_FILE, "w") as f:                 f.write(json.dumps(self.db, indent=2, sort_keys=False))             print("Created preferences file")       def get(self, *keys, db=None):         if not db: db = self.db         for key in keys:             db = db[key]         return db       def load(self):         with open(PREFERENCES_FILE, "r") as f:             self.db = json.load(f)         print("Loaded preferences database")       def repair(self, db, default=PREFERENCES_DEFAULT):         for key in default:             if isinstance(default[key], dict):                 self.repair(db[key], default[key])             else:                 db.setdefault(key, default[key])       def save(self):         with open(PREFERENCES_FILE, "w") as f:             f.write(json.dumps(self.db, indent=2, sort_keys=False))         print("Saved preferences database")       def validate(self):         old = dict(self.db)         self.repair(self.db)         if not self.db == old:             print("Repaired missing keys in database")             self.save()     with open(PREFERENCES_FILE, "w") as f:     f.write(json.dumps(PREFERENCES_BROKEN, indent=2, sort_keys=False))     #f.write(json.dumps(PREFERENCES_DEFAULT, indent=2, sort_keys=False))   db = Database() print(db.get("Key A", "sub key", "value")) print(db.get("Key B", "value")) print(db.get("Key C"))