Fix MAX_TIMESTAMP calculation in non-UTC timezones (#1159)

arrow/constants.py

@@ -1,27 +1,24 @@
 """Constants used internally in arrow."""
 
 import sys
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Final
 
-# datetime.max.timestamp() errors on Windows, so we must hardcode
-# the highest possible datetime value that can output a timestamp.
-# tl;dr platform-independent max timestamps are hard to form
-# See: https://stackoverflow.com/q/46133223
+# datetime.max.replace(tzinfo=timezone.utc).timestamp() gives the platform-independent
+# max POSIX timestamp. Without tzinfo=timezone.utc, datetime.max.timestamp() raises
+# OverflowError or ValueError ("year 10000 is out of range") in timezones ahead of UTC.
 try:
-    # Get max timestamp. Works on POSIX-based systems like Linux and macOS,
-    # but will trigger an OverflowError, ValueError, or OSError on Windows
-    _MAX_TIMESTAMP = datetime.max.timestamp()
+    _MAX_TIMESTAMP = datetime.max.replace(tzinfo=timezone.utc).timestamp()
 except (OverflowError, ValueError, OSError):  # pragma: no cover
     # Fallback for Windows and 32-bit systems if initial max timestamp call fails
     # Must get max value of ctime on Windows based on architecture (x32 vs x64)
     # https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/ctime-ctime32-ctime64-wctime-wctime32-wctime64
     # Note: this may occur on both 32-bit Linux systems (issue #930) along with Windows systems
     is_64bits = sys.maxsize > 2**32
     _MAX_TIMESTAMP = (
-        datetime(3000, 1, 1, 23, 59, 59, 999999).timestamp()
+        datetime(3000, 1, 1, 23, 59, 59, 999999, tzinfo=timezone.utc).timestamp()
         if is_64bits
-        else datetime(2038, 1, 1, 23, 59, 59, 999999).timestamp()
+        else datetime(2038, 1, 1, 23, 59, 59, 999999, tzinfo=timezone.utc).timestamp()
     )
 
 MAX_TIMESTAMP: Final[float] = _MAX_TIMESTAMP

tests/test_util.py

@@ -122,6 +122,10 @@ def test_normalize_timestamp(self):
         assert util.normalize_timestamp(millisecond_timestamp) == 1591161115.194
         assert util.normalize_timestamp(microsecond_timestamp) == 1591161115.194556
 
+        # Test timestamp for year 9999-12-31 is not mistakenly divided by 1000
+        max_year_ts = 253402214400.0
+        assert util.normalize_timestamp(max_year_ts) == max_year_ts
+
         with pytest.raises(ValueError):
             util.normalize_timestamp(3e17)