Extra CubeAttrsDict methods to emulate dictionary behaviours.

lib/iris/cube.py

@@ -972,7 +972,11 @@ def __eq__(self, other):
         return result
 
     #
-    # Provide a copy method, as for 'dict', but *not* provided by MutableMapping
+    # Provide methods duplicating those for a 'dict', but which are *not* provided by
+    # MutableMapping, for compatibility with code which expected a cube.attributes to be
+    # a :class:`~iris.common.mixin.LimitedAttributeDict`.
+    # The extra required methods are :
+    #   'copy', 'update', '__ior__', '__or__', '__ror__' and 'fromkeys'.
     #
     def copy(self):
         """
@@ -983,6 +987,66 @@ def copy(self):
         """
         return CubeAttrsDict(self)
 
+    def update(self, *args, **kwargs):
+        """
+        Update by adding items from a mapping arg, or keyword-values.
+
+        If the argument is a split dictionary, preserve the local/global nature of its
+        keys.
+        """
+        if args and hasattr(args[0], "globals") and hasattr(args[0], "locals"):
+            dic = args[0]
+            self.globals.update(dic.globals)
+            self.locals.update(dic.locals)
+        else:
+            super().update(*args)
+        super().update(**kwargs)
+
+    def __or__(self, arg):
+        """Implement 'or' via 'update'."""
+        if not isinstance(arg, Mapping):
+            return NotImplemented
+        new_dict = self.copy()
+        new_dict.update(arg)
+        return new_dict
+
+    def __ior__(self, arg):
+        """Implement 'ior' via 'update'."""
+        self.update(arg)
+        return self
+
+    def __ror__(self, arg):
+        """
+        Implement 'ror' via 'update'.
+
+        This needs to promote, such that the result is a CubeAttrsDict.
+        """
+        if not isinstance(arg, Mapping):
+            return NotImplemented
+        result = CubeAttrsDict(arg)
+        result.update(self)
+        return result
+
+    @classmethod
+    def fromkeys(cls, iterable, value=None):
+        """
+        Create a new object with keys taken from an argument, all set to one value.
+
+        If the argument is a split dictionary, preserve the local/global nature of its
+        keys.
+        """
+        if hasattr(iterable, "globals") and hasattr(iterable, "locals"):
+            # When main input is a split-attrs dict, create global/local parts from its
+            # global/local keys
+            result = cls(
+                globals=dict.fromkeys(iterable.globals, value),
+                locals=dict.fromkeys(iterable.locals, value),
+            )
+        else:
+            # Create from a dict.fromkeys, using default classification of the keys.
+            result = cls(dict.fromkeys(iterable, value))
+        return result
+
     #
     # The remaining methods are sufficient to generate a complete standard Mapping
     # API.  See -

lib/iris/tests/unit/cube/test_CubeAttrsDict.py

@@ -23,8 +23,17 @@ def sample_attrs() -> CubeAttrsDict:
 
 
 def check_content(attrs, locals=None, globals=None, matches=None):
-    # Check a CubeAttrsDict for expected properties.
-    # If locals/globals are set, test for equality and non-identity.
+    """
+    Check a CubeAttrsDict for expected properties.
+
+    Its ".globals" and ".locals" must match 'locals' and 'globals' args
+    -- except that, if 'matches' is provided, it is a CubeAttrsDict, whose
+    locals/globals *replace* the 'locals'/'globals' arguments.
+
+    Check that the result is a CubeAttrsDict and, for both local + global parts,
+      * parts match for *equality* (==) but are *non-identical* (is not)
+      * order of keys matches expected (N.B. which is *not* required for equality)
+    """
     assert isinstance(attrs, CubeAttrsDict)
     attr_locals, attr_globals = attrs.locals, attrs.globals
     assert type(attr_locals) == LimitedAttributeDict
@@ -41,6 +50,7 @@ def check(arg, content):
         # .. we proceed to ensure that the stored content is equal but NOT the same
         assert content == arg
         assert content is not arg
+        assert list(content.keys()) == list(arg.keys())
 
     check(locals, attr_locals)
     check(globals, attr_globals)
@@ -98,14 +108,89 @@ def test_copy(self, sample_attrs):
         assert copy is not sample_attrs
         check_content(copy, matches=sample_attrs)
 
-    def test_update(self, sample_attrs):
-        updated = sample_attrs.copy()
-        updated.update({"q": 77})
-        expected_locals = sample_attrs.locals.copy()
-        expected_locals["q"] = 77
-        check_content(
-            updated, globals=sample_attrs.globals, locals=expected_locals
+    @pytest.fixture(params=["regular_arg", "split_arg"])
+    def update_testcase(self, request):
+        lhs = CubeAttrsDict(globals={"a": 1, "b": 2}, locals={"b": 3, "c": 4})
+        if request.param == "split_arg":
+            # A set of "update settings", with global/local-specific keys.
+            rhs = CubeAttrsDict(
+                globals={"a": 1001, "x": 1007},
+                # NOTE: use a global-default key here, to check that type is preserved
+                locals={"b": 1003, "history": 1099},
+            )
+            expected_result = CubeAttrsDict(
+                globals={"a": 1001, "b": 2, "x": 1007},
+                locals={"b": 1003, "c": 4, "history": 1099},
+            )
+        else:
+            assert request.param == "regular_arg"
+            # A similar set of update values in a regular dict (so not local/global)
+            rhs = {"a": 1001, "x": 1007, "b": 1003, "history": 1099}
+            expected_result = CubeAttrsDict(
+                globals={"a": 1001, "b": 2, "history": 1099},
+                locals={"b": 1003, "c": 4, "x": 1007},
+            )
+        return lhs, rhs, expected_result
+
+    def test_update(self, update_testcase):
+        testval, updater, expected = update_testcase
+        testval.update(updater)
+        check_content(testval, matches=expected)
+
+    def test___or__(self, update_testcase):
+        testval, updater, expected = update_testcase
+        original = testval.copy()
+        result = testval | updater
+        assert result is not testval
+        assert testval == original
+        check_content(result, matches=expected)
+
+    def test___ior__(self, update_testcase):
+        testval, updater, expected = update_testcase
+        testval |= updater
+        check_content(testval, matches=expected)
+
+    def test___ror__(self):
+        # Check the "or" operation, when lhs is a regular dictionary
+        lhs = {"a": 1, "b": 2, "history": 3}
+        rhs = CubeAttrsDict(
+            globals={"a": 1001, "x": 1007},
+            # NOTE: use a global-default key here, to check that type is preserved
+            locals={"b": 1003, "history": 1099},
         )
+        # The lhs should be promoted to a CubeAttrsDict, and then combined.
+        expected = CubeAttrsDict(
+            globals={"history": 3, "a": 1001, "x": 1007},
+            locals={"a": 1, "b": 1003, "history": 1099},
+        )
+        result = lhs | rhs
+        check_content(result, matches=expected)
+
+    @pytest.mark.parametrize("value", [1, None])
+    @pytest.mark.parametrize("inputtype", ["regular_arg", "split_arg"])
+    def test__fromkeys(self, value, inputtype):
+        if inputtype == "regular_arg":
+            # Check when input is a plain iterable of key-names
+            keys = ["a", "b", "history"]
+            # Result has keys assigned local/global via default mechanism.
+            expected = CubeAttrsDict(
+                globals={"history": value},
+                locals={"a": value, "b": value},
+            )
+        else:
+            assert inputtype == "split_arg"
+            # Check when input is a CubeAttrsDict
+            keys = CubeAttrsDict(
+                globals={"a": 1}, locals={"b": 2, "history": 3}
+            )
+            # The result preserves the input keys' local/global identity
+            # N.B. "history" would be global by default (cf. "regular_arg" case)
+            expected = CubeAttrsDict(
+                globals={"a": value},
+                locals={"b": value, "history": value},
+            )
+        result = CubeAttrsDict.fromkeys(keys, value)
+        check_content(result, matches=expected)
 
     def test_to_dict(self, sample_attrs):
         result = dict(sample_attrs)