Add time-zone aware timestamp normalization transformer with tests

petl/test/transform/test_normalize_timezone.py

@@ -0,0 +1,27 @@
+import unittest
+from petl.transform.normalize_timezone import normalize_timezone
+
+class TestNormalizeTimezone(unittest.TestCase):
+
+    def test_basic_conversion(self):
+        input_data = [
+            {'timestamp': '2023-12-01T10:00:00', 'timezone': 'America/New_York'},
+            {'timestamp': '2023-12-01T15:00:00', 'timezone': 'Europe/London'}
+        ]
+        result = list(normalize_timezone(input_data))
+        self.assertEqual(result[0]['timestamp_utc'], '2023-12-01T15:00:00+00:00')
+        self.assertEqual(result[1]['timestamp_utc'], '2023-12-01T15:00:00+00:00')
+        self.assertEqual(result[0]['timezone_original'], 'America/New_York')
+
+    def test_invalid_timezone(self):
+        input_data = [{'timestamp': '2023-12-01T10:00:00', 'timezone': 'Invalid/Zone'}]
+        with self.assertRaises(ValueError):
+            list(normalize_timezone(input_data))
+
+    def test_missing_timestamp(self):
+        input_data = [{'timezone': 'UTC'}]
+        with self.assertRaises(ValueError):
+            list(normalize_timezone(input_data))
+
+if __name__ == '__main__':
+    unittest.main()

petl/transform/normalize_timezone.py

@@ -0,0 +1,38 @@
+from datetime import datetime
+import pytz
+
+def normalize_timezone(table, timestamp_col='timestamp', tz_col='timezone'):
+    """
+    Normalize timestamps to UTC while retaining original timezone.
+
+    Args:
+        table: petl table (iterable of rows/dicts)
+        timestamp_col (str): column name with timestamp strings
+        tz_col (str): column name with timezone name (e.g., 'America/New_York')
+
+    Yields:
+        Each row with two added fields: 'timestamp_utc' and 'timezone_original'
+    """
+    for row in table:
+        try:
+            original_ts = row[timestamp_col]
+            original_tz = row[tz_col]
+
+            # Parse the timestamp
+            naive_dt = datetime.fromisoformat(original_ts)
+
+            # Attach original timezone
+            local_dt = pytz.timezone(original_tz).localize(naive_dt)
+
+            # Convert to UTC
+            utc_dt = local_dt.astimezone(pytz.UTC)
+
+            # Create a new row with original + new fields
+            new_row = dict(row)
+            new_row['timestamp_utc'] = utc_dt.isoformat()
+            new_row['timezone_original'] = original_tz
+
+            yield new_row
+
+        except Exception as e:
+            raise ValueError(f"Failed to normalize row {row} due to error: {e}")