Ensure caches are removed from what is pickled

astropy/time/core.py

@@ -1653,6 +1653,12 @@ def cache(self):
         for instance in self._id_cache.values():
             del instance._time.cache
 
+    def __getstate__(self):
+        # For pickling, we remove the cache from what's pickled
+        state = super().__getstate__().copy()
+        state.pop("_id_cache", None)
+        return state
+
     def __getattr__(self, attr):
         """
         Get dynamic attributes to output format or do timescale conversion.

astropy/time/formats.py

@@ -288,6 +288,12 @@ def cache(self):
         """
         return defaultdict(dict)
 
+    def __getstate__(self):
+        # For pickling, we remove the cache.
+        state = super().__getstate__().copy()
+        state.pop("cache", None)
+        return state
+
     def _check_val_type(self, val1, val2):
         """Input value validation, typically overridden by derived classes."""
         # val1 cannot contain nan, but val2 can contain nan

astropy/time/tests/test_pickle.py

@@ -25,3 +25,17 @@ def test_pickle(self):
             t2d = pickle.dumps(t2, prot)
             t2l = pickle.loads(t2d)
             assert t2l == t2
+
+    def test_cache_not_shared(self):
+        t = Time(["2001:020", "2001:040", "2001:060", "2001:080"], out_subfmt="date")
+        # Ensure something is in the cache.
+        t.value
+        assert "format" in t.cache
+        td = pickle.dumps(t)
+        assert "format" in t.cache
+        tl = pickle.loads(td)
+        assert "format" in t.cache
+        assert "format" not in tl.cache
+        t[0] = "1999:099"
+        assert t.value[0] == "1999:099"
+        assert tl.value[0] == "2001:020"