Persistent state

diff --git a/persistent_state.py b/persistent_state.py
new file mode 100644 (file)
index 0000000..1607b5e
--- /dev/null
+++ b/persistent_state.py
@@ -0,0 +1,51 @@
+#!/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))

diff --git a/tests/persistent_state_test.py b/tests/persistent_state_test.py
new file mode 100755 (executable)
index 0000000..f9afdde
--- /dev/null
+++ b/tests/persistent_state_test.py
@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+
+import os
+import unittest
+
+import bootstrap
+import persistent_state as ps
+
+import unittest_utils as uu
+
+
+class TestPersistentState(unittest.TestCase):
+    def test_it_all_baby(self):
+        filename = '/tmp/.persistent_state_test.bin'
+        os.system(f'/bin/rm {filename}')
+        s = ps.PersistentState(filename)
+        self.assertEqual(0, len(s))
+        s['test'] = 123
+        self.assertEqual(123, s['test'])
+        self.assertEqual(1, len(s))
+        s['ing'] = 234
+        self.assertEqual(2, len(s))
+        del s['ing']
+        self.assertEqual(1, len(s))
+        s.save()
+        t = ps.PersistentState(filename)
+        self.assertEqual(1, len(t))
+        self.assertEqual(123, t['test'])
+
+
+if __name__ == '__main__':
+    bootstrap.initialize(unittest.main)()
+