persistent_state.py

   1 #!/usr/bin/env python3
   2
   3 import pickle
   4 from typing import Any, Mapping
   5
   6 import file_utils
   7
   8
   9 class PersistentState(object):
  10     """
  11     An object that behaves like a persistent hash map; it can be
  12     accessed to store key-value pairs but also saved to disk and read
  13     back from disk easily.
  14
  15     """
  16     def __init__(self, filename: str, *, max_age_sec: int = None):
  17         self.filename = filename
  18         if file_utils.does_file_exist(self.filename):
  19             if max_age_sec is not None:
  20                 age = file_utils.get_file_mtime_age_seconds(self.filename)
  21                 if age < max_age_sec:
  22                     self.state = self.load()
  23                 else:
  24                     self.state = {}
  25             else:
  26                 self.state = self.load()
  27         else:
  28             self.state = {}
  29
  30     def __getitem__(self, key: str) -> Any:
  31         return self.state.get(key, "")
  32
  33     def __setitem__(self, key: str, value: Any):
  34         self.state[key] = value
  35
  36     def __delitem__(self, key: str):
  37         del self.state[key]
  38
  39     def __iter__(self):
  40         return iter(self.state)
  41
  42     def __len__(self):
  43         return len(self.state)
  44
  45     def save(self) -> None:
  46         with open(self.filename, 'wb') as f:
  47             pickle.dump(self.state, f, pickle.HIGHEST_PROTOCOL)
  48
  49     def load(self) -> Mapping[str, Any]:
  50         with open(self.filename, 'rb') as f:
  51             return(pickle.load(f))