ORM: Implement the Dict.get method (#6200)

This makes the behavior of `Dict` identical to that of a plain `dict`
with respect to this method. The `Dict` class inherited the `get` method
from the `Entity` base class, but that has a completely different
purpose that is not of interest for users of the `Dict` class.

aiida/orm/nodes/data/dict.py

@@ -8,7 +8,10 @@
 # For further information please visit http://www.aiida.net               #
 ###########################################################################
 """`Data` sub class to represent a dictionary."""
+from __future__ import annotations
+
 import copy
+import typing as t
 
 from aiida.common import exceptions
 
@@ -79,6 +82,15 @@ def __contains__(self, key: str) -> bool:
         """Return whether the node contains a key."""
         return key in self.base.attributes
 
+    def get(self, key: str, default: t.Any | None = None, /):  # type: ignore[override]  # pylint: disable=arguments-differ
+        """Return the value for key if key is in the dictionary, else default.
+
+        :param key: The key whose value to return.
+        :param default: Optional default to return in case the key does not exist.
+        :returns: The value if the key exists, otherwise the ``default``.
+        """
+        return self.base.attributes.get(key, default)
+
     def set_dict(self, dictionary):
         """Replace the current dictionary with another one.
 

tests/orm/nodes/data/test_dict.py

@@ -44,6 +44,15 @@ def test_dict_property(dictionary):
     assert node.dict.nested == dictionary['nested']
 
 
+def test_get(dictionary):
+    """Test the ``get`` method."""
+    node = Dict(dictionary)
+    assert node.get('invalid') is None
+    assert node.get('invalid', 'default') == 'default'
+    assert node.get('value') == dictionary['value']
+    assert node.get('nested') == dictionary['nested']
+
+
 def test_get_item(dictionary):
     """Test the ``__getitem__`` method."""
     node = Dict(dictionary)