From 12901c286d55f1ae6bfd669eaee5231d6ef6ecdd Mon Sep 17 00:00:00 2001
From: Glyph <code@glyph.im>
Date: Sun, 5 Oct 2025 00:33:41 -0700
Subject: [PATCH] adjust `DateTime.__sub__` to allow differing tzinfo
 implementations

Fixes #17

This commit was sponsored by Blaise Pabon, Amethyst Reese, and my
other patrons.  If you want to join them, you can support my work at
https://glyph.im/patrons/.
---
 expected_mypy.txt                  | 16 +++++++++++++++-
 expected_mypy_37.txt               | 16 +++++++++++++++-
 src/datetype/__init__.py           |  5 ++++-
 src/datetype/test/test_datetype.py | 24 +++++++++++++++++++++++-
 tryit.py                           |  5 +++++
 5 files changed, 62 insertions(+), 4 deletions(-)

diff --git a/expected_mypy.txt b/expected_mypy.txt
index 1f8eb77..3eeee02 100644
--- a/expected_mypy.txt
+++ b/expected_mypy.txt
@@ -44,4 +44,18 @@ tryit.py:53: note:     Got:
 tryit.py:53: note:         def timetz(self) -> Time[timezone]
 tryit.py:53: note:     tzinfo: expected "None", got "timezone"
 tryit.py:56: error: Incompatible types in assignment (expression has type "NaiveTime", variable has type "DateTime[timezone]")  [assignment]
-Found 10 errors in 1 file (checked 1 source file)
+tryit.py:58: error: Unsupported operand types for - ("NaiveDateTime" and "AwareDateTime")  [operator]
+tryit.py:58: note: Following member(s) of "AwareDateTime" have conflicts:
+tryit.py:58: note:     Expected:
+tryit.py:58: note:         def timetz(self) -> Time[None]
+tryit.py:58: note:     Got:
+tryit.py:58: note:         def timetz(self) -> Time[tzinfo]
+tryit.py:58: note:     tzinfo: expected "None", got "tzinfo"
+tryit.py:59: error: Unsupported operand types for - ("AwareDateTime" and "NaiveDateTime")  [operator]
+tryit.py:59: note: Following member(s) of "NaiveDateTime" have conflicts:
+tryit.py:59: note:     Expected:
+tryit.py:59: note:         def timetz(self) -> Time[tzinfo]
+tryit.py:59: note:     Got:
+tryit.py:59: note:         def timetz(self) -> Time[None]
+tryit.py:59: note:     tzinfo: expected "tzinfo", got "None"
+Found 12 errors in 1 file (checked 1 source file)
diff --git a/expected_mypy_37.txt b/expected_mypy_37.txt
index 386e580..c7e3767 100644
--- a/expected_mypy_37.txt
+++ b/expected_mypy_37.txt
@@ -30,4 +30,18 @@ tryit.py:53: note:     Got:
 tryit.py:53: note:         def timetz(self) -> Time[timezone]
 tryit.py:53: note:     tzinfo: expected "None", got "timezone"
 tryit.py:56: error: Incompatible types in assignment (expression has type "NaiveTime", variable has type "DateTime[timezone]")  [assignment]
-Found 8 errors in 1 file (checked 1 source file)
+tryit.py:58: error: Unsupported operand types for - ("NaiveDateTime" and "AwareDateTime")  [operator]
+tryit.py:58: note: Following member(s) of "AwareDateTime" have conflicts:
+tryit.py:58: note:     Expected:
+tryit.py:58: note:         def timetz(self) -> Time[None]
+tryit.py:58: note:     Got:
+tryit.py:58: note:         def timetz(self) -> Time[tzinfo]
+tryit.py:58: note:     tzinfo: expected "None", got "tzinfo"
+tryit.py:59: error: Unsupported operand types for - ("AwareDateTime" and "NaiveDateTime")  [operator]
+tryit.py:59: note: Following member(s) of "NaiveDateTime" have conflicts:
+tryit.py:59: note:     Expected:
+tryit.py:59: note:         def timetz(self) -> Time[tzinfo]
+tryit.py:59: note:     Got:
+tryit.py:59: note:         def timetz(self) -> Time[None]
+tryit.py:59: note:     tzinfo: expected "tzinfo", got "None"
+Found 10 errors in 1 file (checked 1 source file)
diff --git a/src/datetype/__init__.py b/src/datetype/__init__.py
index a4f2d7c..8a9c680 100644
--- a/src/datetype/__init__.py
+++ b/src/datetype/__init__.py
@@ -456,7 +456,10 @@ def __gt__(self: Self, __other: Self) -> bool: ...
     def __sub__(self: Self, __other: _timedelta) -> Self: ...
 
     @overload
-    def __sub__(self: DTSelf, __other: DTSelf) -> _timedelta: ...
+    def __sub__(self: DateTime[None], __other: DateTime[None]) -> _timedelta: ...
+
+    @overload
+    def __sub__(self: DateTime[_tzinfo], __other: DateTime[_tzinfo]) -> _timedelta: ...
 
     def __add__(self: Self, __other: _timedelta) -> Self: ...
 
diff --git a/src/datetype/test/test_datetype.py b/src/datetype/test/test_datetype.py
index 352a800..6d42cbd 100644
--- a/src/datetype/test/test_datetype.py
+++ b/src/datetype/test/test_datetype.py
@@ -4,7 +4,15 @@
 from sys import version_info
 from unittest import TestCase, skipIf
 
-from datetype import AwareDateTime, NaiveDateTime, NaiveTime, Time, aware, naive
+from datetype import (
+    AwareDateTime,
+    NaiveDateTime,
+    NaiveTime,
+    Time,
+    aware,
+    naive,
+    DateTime,
+)
 
 TEST_DATA = (Path(__file__) / "..").resolve()
 while not (TEST_DATA / ".git").is_dir():
@@ -87,3 +95,17 @@ def test_none_aware(self) -> None:
         awareified = aware(stddt)
         self.assertIs(awareified.tzinfo, zi)
         self.assertEqual(awareified.tzinfo.dst(stddt), timedelta(0))
+
+    @skipIf(version_info < (3, 9), "ZoneInfo")
+    def test_differing_zone_subtract(self) -> None:
+        from zoneinfo import ZoneInfo
+
+        zi = ZoneInfo("US/Pacific")
+        stddt = datetime(2025, 2, 13, 15, 35, 13, 574354, tzinfo=zi)
+        inutc = stddt.astimezone(timezone.utc)
+
+        dtzi: DateTime[ZoneInfo] = aware(stddt, ZoneInfo)
+        dttz: DateTime[timezone] = aware(inutc, timezone)
+
+        self.assertEqual(dtzi - dttz, timedelta(0))
+        self.assertEqual(dttz - dtzi, timedelta(0))
diff --git a/tryit.py b/tryit.py
index 0a796e0..b7c4845 100644
--- a/tryit.py
+++ b/tryit.py
@@ -54,3 +54,8 @@
 is_aware: DateTime[timezone] = a.astimezone(None)
 
 not_aware_method_time: DateTime[timezone] = a.time()  # nope; actually naive
+
+x - y                           # error; naive & aware are incompatible
+y - x                           # also error
+y - is_aware                    # ok
+is_aware - y                    # ok