FIX: Retain original timezone in Python datetime objects (microsoft#281)

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### Summary   
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This pull request updates how `datetimeoffset` values are handled when
reading from SQL Server in the Python bindings. The main change is to
preserve the original timezone information in returned Python `datetime`
objects, instead of always converting them to UTC. Correspondingly, the
test suite has been updated to compare datetimes with their original
timezone rather than converting to UTC for assertions.

**Datetimeoffset handling improvements:**

* Removed forced conversion of `datetimeoffset` values to UTC in
`SQLGetData_wrap` and `FetchBatchData`, so Python datetime objects
retain their original timezone info.
[[1]](diffhunk://#diff-dde2297345718ec449a14e7dff91b7bb2342b008ecc071f562233646d71144a1L2808)
[[2]](diffhunk://#diff-dde2297345718ec449a14e7dff91b7bb2342b008ecc071f562233646d71144a1L3321)

**Test suite updates:**

* Updated all relevant tests in `tests/test_004_cursor.py` to compare
datetimes directly, preserving timezone information, instead of
converting to UTC for equality checks. This affects tests for
read/write, max/min offsets, DST transitions, executemany, and extreme
offsets.
[[1]](diffhunk://#diff-82594712308ff34afa8b067af67db231e9a1372ef474da3db121e14e4d418f69L7890-R7890)
[[2]](diffhunk://#diff-82594712308ff34afa8b067af67db231e9a1372ef474da3db121e14e4d418f69L7929-R7924)
[[3]](diffhunk://#diff-82594712308ff34afa8b067af67db231e9a1372ef474da3db121e14e4d418f69L7989-R7979)
[[4]](diffhunk://#diff-82594712308ff34afa8b067af67db231e9a1372ef474da3db121e14e4d418f69L8071-R8056)
[[5]](diffhunk://#diff-82594712308ff34afa8b067af67db231e9a1372ef474da3db121e14e4d418f69L8147-R8122)
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Author: gargsaumya

mssql_python/pybind/ddbc_bindings.cpp

@@ -2805,7 +2805,6 @@ SQLRETURN SQLGetData_wrap(SqlHandlePtr StatementHandle, SQLUSMALLINT colCount, p
                         microseconds,
                         tzinfo
                     );
-                    py_dt = py_dt.attr("astimezone")(datetime.attr("timezone").attr("utc"));
                     row.append(py_dt);
                 } else {
                     LOG("Error fetching DATETIMEOFFSET for column {}, ret={}", i, ret);
@@ -3318,7 +3317,6 @@ SQLRETURN FetchBatchData(SQLHSTMT hStmt, ColumnBuffers& buffers, py::list& colum
                             dtoValue.fraction / 1000,  // ns → µs
                             tzinfo
                         );
-                        py_dt = py_dt.attr("astimezone")(datetime.attr("timezone").attr("utc"));
                         row.append(py_dt);
                     } else {
                         row.append(py::none());

tests/test_004_cursor.py

@@ -7887,12 +7887,7 @@ def test_datetimeoffset_read_write(cursor, db_connection):
             assert row is not None
             fetched_id, fetched_dt = row
             assert fetched_dt.tzinfo is not None
-            expected_utc = dt.astimezone(timezone.utc)
-            fetched_utc = fetched_dt.astimezone(timezone.utc)
-            # Ignore sub-microsecond differences
-            expected_utc = expected_utc.replace(microsecond=int(expected_utc.microsecond / 1000) * 1000)
-            fetched_utc = fetched_utc.replace(microsecond=int(fetched_utc.microsecond / 1000) * 1000)
-            assert fetched_utc == expected_utc
+            assert fetched_dt == dt
     finally:
         cursor.execute("DROP TABLE IF EXISTS #pytest_datetimeoffset_read_write;")
         db_connection.commit()
@@ -7926,12 +7921,7 @@ def test_datetimeoffset_max_min_offsets(cursor, db_connection):
             assert fetched_id == expected_id, f"ID mismatch: expected {expected_id}, got {fetched_id}"
             assert fetched_dt.tzinfo is not None, f"Fetched datetime object is naive for id {fetched_id}"
 
-            # Compare in UTC to avoid offset differences
-            expected_utc = expected_dt.astimezone(timezone.utc).replace(tzinfo=None)
-            fetched_utc = fetched_dt.astimezone(timezone.utc).replace(tzinfo=None)
-            assert fetched_utc == expected_utc, (
-                f"Value mismatch for id {expected_id}: expected UTC {expected_utc}, got {fetched_utc}"
-            )
+            assert fetched_dt == expected_dt, f"Value mismatch for id {expected_id}: expected {expected_dt}, got {fetched_dt}"
 
     finally:
         cursor.execute("DROP TABLE IF EXISTS #pytest_datetimeoffset_read_write;")
@@ -7986,12 +7976,7 @@ def test_datetimeoffset_dst_transitions(cursor, db_connection):
             assert fetched_id == expected_id, f"ID mismatch: expected {expected_id}, got {fetched_id}"
             assert fetched_dt.tzinfo is not None, f"Fetched datetime object is naive for id {fetched_id}"
 
-            # Compare UTC time to avoid issues due to offsets changing in DST
-            expected_utc = expected_dt.astimezone(timezone.utc).replace(tzinfo=None)
-            fetched_utc = fetched_dt.astimezone(timezone.utc).replace(tzinfo=None)
-            assert fetched_utc == expected_utc, (
-                f"Value mismatch for id {expected_id}: expected UTC {expected_utc}, got {fetched_utc}"
-            )
+            assert fetched_dt == expected_dt, f"Value mismatch for id {expected_id}: expected {expected_dt}, got {fetched_dt}"
 
     finally:
         cursor.execute("DROP TABLE IF EXISTS #pytest_datetimeoffset_dst_transitions;")
@@ -8068,17 +8053,7 @@ def test_datetimeoffset_executemany(cursor, db_connection):
             fetched_id, fetched_dto = rows[i]
             assert fetched_dto.tzinfo is not None, "Fetched datetime object is naive."
 
-            expected_utc = python_dt.astimezone(timezone.utc).replace(tzinfo=None)
-            fetched_utc = fetched_dto.astimezone(timezone.utc).replace(tzinfo=None)
-
-            # Round microseconds to nearest millisecond for comparison
-            expected_utc = expected_utc.replace(microsecond=int(expected_utc.microsecond / 1000) * 1000)
-            fetched_utc = fetched_utc.replace(microsecond=int(fetched_utc.microsecond / 1000) * 1000)
-
-            assert fetched_utc == expected_utc, (
-                f"Value mismatch for test case {i}. "
-                f"Expected UTC: {expected_utc}, Got UTC: {fetched_utc}"
-            )
+            assert fetched_dto == python_dt, f"Value mismatch for id {fetched_id}: expected {python_dt}, got {fetched_dto}"
     finally:
         cursor.execute("IF OBJECT_ID('tempdb..#pytest_dto', 'U') IS NOT NULL DROP TABLE #pytest_dto;")
         db_connection.commit()
@@ -8144,13 +8119,44 @@ def test_datetimeoffset_extreme_offsets(cursor, db_connection):
         for i, dt in enumerate(extreme_offsets):
             _, fetched = rows[i]
             assert fetched.tzinfo is not None
-            # Round-trip comparison via UTC
-            expected_utc = dt.astimezone(timezone.utc).replace(tzinfo=None)
-            fetched_utc = fetched.astimezone(timezone.utc).replace(tzinfo=None)
-            assert expected_utc == fetched_utc, f"Extreme offset round-trip failed for {dt.tzinfo}"
+            assert fetched == dt, f"Value mismatch for id {i}: expected {dt}, got {fetched}"
     finally:
         cursor.execute("IF OBJECT_ID('tempdb..#pytest_dto', 'U') IS NOT NULL DROP TABLE #pytest_dto;")
         db_connection.commit()
+        
+def test_datetimeoffset_native_vs_string_simple(cursor, db_connection):
+    """
+    Replicates the user's testing scenario: fetch DATETIMEOFFSET as native datetime
+    and as string using CONVERT(nvarchar(35), ..., 121).
+    """
+    try:
+        cursor.execute("CREATE TABLE #pytest_dto_user_test (id INT PRIMARY KEY, Systime DATETIMEOFFSET);")
+        db_connection.commit()
+
+        # Insert rows similar to user's example
+        test_rows = [
+            (1, datetime(2025, 5, 14, 12, 35, 52, 501000, tzinfo=timezone(timedelta(hours=1)))),
+            (2, datetime(2025, 5, 14, 15, 20, 30, 123000, tzinfo=timezone(timedelta(hours=-5))))
+        ]
+
+        for i, dt in test_rows:
+            cursor.execute("INSERT INTO #pytest_dto_user_test (id, Systime) VALUES (?, ?);", i, dt)
+        db_connection.commit()
+
+        # Native fetch (like the user's first execute)
+        cursor.execute("SELECT Systime FROM #pytest_dto_user_test WHERE id=1;")
+        dt_native = cursor.fetchone()[0]
+        assert dt_native.tzinfo is not None
+        assert dt_native == test_rows[0][1]
+
+        # String fetch (like the user's convert to nvarchar)
+        cursor.execute("SELECT CONVERT(nvarchar(35), Systime, 121) FROM #pytest_dto_user_test WHERE id=1;")
+        dt_str = cursor.fetchone()[0]
+        assert dt_str.endswith("+01:00")  # original offset preserved
+
+    finally:
+        cursor.execute("DROP TABLE IF EXISTS #pytest_dto_user_test;")
+        db_connection.commit()
 
 def test_lowercase_attribute(cursor, db_connection):
     """Test that the lowercase attribute properly converts column names to lowercase"""