[DeferredDict] implement get/items/values for deferreddict

masque/test/test_utils.py

@@ -2,7 +2,7 @@ import numpy
 from numpy.testing import assert_equal, assert_allclose
 from numpy import pi
 
-from ..utils import remove_duplicate_vertices, remove_colinear_vertices, poly_contains_points, rotation_matrix_2d, apply_transforms
+from ..utils import remove_duplicate_vertices, remove_colinear_vertices, poly_contains_points, rotation_matrix_2d, apply_transforms, DeferredDict
 
 
 def test_remove_duplicate_vertices() -> None:
@@ -86,3 +86,21 @@ def test_apply_transforms_advanced() -> None:
     # 2. rotate by outer rotation (pi/2): (10, 0) -> (0, 10)
     # 3. add outer offset (0, 0) -> (0, 10)
     assert_allclose(combined[0], [0, 10, pi / 2, 1, 1], atol=1e-10)
+
+
+def test_deferred_dict_accessors_resolve_values_once() -> None:
+    calls = 0
+
+    def make_value() -> int:
+        nonlocal calls
+        calls += 1
+        return 7
+
+    deferred = DeferredDict[str, int]()
+    deferred["x"] = make_value
+
+    assert deferred.get("missing", 9) == 9
+    assert deferred.get("x") == 7
+    assert list(deferred.values()) == [7]
+    assert list(deferred.items()) == [("x", 7)]
+    assert calls == 1

masque/utils/deferreddict.py

@@ -1,5 +1,5 @@
 from typing import TypeVar, Generic
-from collections.abc import Callable
+from collections.abc import Callable, Iterator
 from functools import lru_cache
 
 
@@ -41,6 +41,19 @@ class DeferredDict(dict, Generic[Key, Value]):
     def __getitem__(self, key: Key) -> Value:
         return dict.__getitem__(self, key)()
 
+    def get(self, key: Key, default: Value | None = None) -> Value | None:
+        if key not in self:
+            return default
+        return self[key]
+
+    def items(self) -> Iterator[tuple[Key, Value]]:
+        for key in self.keys():
+            yield key, self[key]
+
+    def values(self) -> Iterator[Value]:
+        for key in self.keys():
+            yield self[key]
+
     def update(self, *args, **kwargs) -> None:
         """
         Update the DeferredDict. If a value is callable, it is used as a generator.