amend_attributes can now add to an existing value, and add timestamps.

improver/metadata/amend.py

@@ -29,6 +29,7 @@
 # ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE.
 """Module containing utilities for modifying cube metadata"""
+import re
 from datetime import datetime, timedelta, timezone
 from typing import Any, Dict, List, Tuple, Union
 
@@ -76,10 +77,25 @@ def amend_attributes(cube: Cube, attributes_dict: Dict[str, Any]) -> None:
             Dictionary containing items of the form {attribute_name: value}.
             The "value" item is either the string "remove" or the new value
             of the attribute required.
+            If the new value contains "{}", the existing value will be
+            inserted at this point (no existing value will result in the
+            "{}" being removed, then applied as the attribute value).
+            If the new value contains "{now:.*}", where the .* is a valid
+            date format, then this string is replaced with the current
+            wall-clock time, formatted as specified.
     """
     for attribute_name, value in attributes_dict.items():
+        re_now = r"({now:.*})"
+        has_now = re.match(rf".*{re_now}.*", value, re.DOTALL)
+        if has_now:
+            now = has_now[1].format(now=datetime.now())
+            value = re.sub(re_now, now, value)
         if value == "remove":
             cube.attributes.pop(attribute_name, None)
+        elif "{}" in value:
+            cube.attributes[attribute_name] = value.format(
+                cube.attributes.get(attribute_name, "")
+            )
         else:
             cube.attributes[attribute_name] = value
 

improver_tests/metadata/test_amend.py

@@ -29,7 +29,7 @@
 # ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE.
 """Tests for the improver.metadata.amend module"""
-
+import re
 import unittest
 from datetime import datetime as dt
 
@@ -128,22 +128,28 @@ def setUp(self):
             attributes={
                 "mosg__grid_version": "1.3.0",
                 "mosg__model_configuration": "uk_det",
+                "history": "20231213T09:04:23Z: StaGE Decoupler",
             },
         )
         self.metadata_dict = {
             "mosg__grid_version": "remove",
             "source": "IMPROVER unit tests",
             "mosg__model_configuration": "other_model",
+            "history": "{}\n{now:%Y%m%dT%H:%M:%SZ}: IMPROVER",
         }
 
     def test_basic(self):
-        """Test function adds, removes and modifies attributes as expected"""
+        """Test function adds, removes, updates and modifies attributes as expected,
+        including the presence of a formatted now string."""
         expected_attributes = {
             "source": "IMPROVER unit tests",
             "mosg__model_configuration": "other_model",
+            "history": "20231213T09:04:23Z: StaGE Decoupler\n.*Z: IMPROVER",
         }
         amend_attributes(self.cube, self.metadata_dict)
-        self.assertDictEqual(self.cube.attributes, expected_attributes)
+        self.assertTrue(self.cube.attributes.keys() == expected_attributes.keys())
+        for k, v in expected_attributes.items():
+            self.assertTrue(re.match(v, self.cube.attributes[k]))
 
 
 class Test_set_history_attribute(IrisTest):