Replace deprecated datetime.utcfromtimestamp and utcnow

commit_msg.txt

@@ -0,0 +1,13 @@
+Replace deprecated datetime.utcfromtimestamp and utcnow
+
+datetime.utcfromtimestamp() and datetime.utcnow() are deprecated
+since Python 3.12 and scheduled for removal. This replaces:
+
+- utcfromtimestamp() in prettyprint.py with
+  datetime.fromtimestamp(ts, tz=timezone.utc), stripping the
+  +00:00 offset so the output stays as before (ISO format + Z)
+
+- utcnow() in a test expression with datetime.now(), since the
+  test only checks that the subtraction produces a timedelta
+
+Fixes #517

eliot/prettyprint.py

@@ -4,7 +4,7 @@
 
 import pprint
 import argparse
-from datetime import datetime
+from datetime import datetime, timezone
 from sys import stdin, stdout
 from collections import OrderedDict
 from json import dumps
@@ -44,16 +44,14 @@
 
 def _render_timestamp(message: dict, local_timezone: bool) -> str:
     """Convert a message's timestamp to a string."""
-    # If we were returning or storing the datetime we'd want to use an
-    # explicit timezone instead of a naive datetime, but since we're
-    # just using it for formatting we needn't bother.
     if local_timezone:
         dt = datetime.fromtimestamp(message[TIMESTAMP_FIELD])
     else:
-        dt = datetime.utcfromtimestamp(message[TIMESTAMP_FIELD])
+        dt = datetime.fromtimestamp(message[TIMESTAMP_FIELD], tz=timezone.utc)
     result = dt.isoformat(sep="T")
     if not local_timezone:
-        result += "Z"
+        # Strip the +00:00 suffix and use Z instead
+        result = result.replace("+00:00", "") + "Z"
     return result
 
 

eliot/tests/test_filter.py

@@ -60,7 +60,7 @@ def test_otherLocals(self):
         built-ins.
         """
         result = self.evaluateExpression(
-            "isinstance(datetime.utcnow() - datetime.utcnow(), timedelta)", {}
+            "isinstance(datetime.now() - datetime.now(), timedelta)", {}
         )
         self.assertEqual(result, True)