+#!/usr/bin/env python3
+
+import pickle
+from typing import Any, Mapping
+
+import file_utils
+
+
+class PersistentState(object):
+ """
+ An object that behaves like a persistent hash map; it can be
+ accessed to store key-value pairs but also saved to disk and read
+ back from disk easily.
+
+ """
+ def __init__(self, filename: str, *, max_age_sec: int = None):
+ self.filename = filename
+ if file_utils.does_file_exist(self.filename):
+ if max_age_sec is not None:
+ age = file_utils.get_file_mtime_age_seconds(self.filename)
+ if age < max_age_sec:
+ self.state = self.load()
+ else:
+ self.state = {}
+ else:
+ self.state = self.load()
+ else:
+ self.state = {}
+
+ def __getitem__(self, key: str) -> Any:
+ return self.state.get(key, "")
+
+ def __setitem__(self, key: str, value: Any):
+ self.state[key] = value
+
+ def __delitem__(self, key: str):
+ del self.state[key]
+
+ def __iter__(self):
+ return iter(self.state)
+
+ def __len__(self):
+ return len(self.state)
+
+ def save(self) -> None:
+ with open(self.filename, 'wb') as f:
+ pickle.dump(self.state, f, pickle.HIGHEST_PROTOCOL)
+
+ def load(self) -> Mapping[str, Any]:
+ with open(self.filename, 'rb') as f:
+ return(pickle.load(f))