[stdlib] Support Dict popitem

docs/changelog.md

@@ -18,6 +18,10 @@ what we publish.
 
 ### ⭐️ New
 
+- `Dict` now support `popitem`, which removes and returns the last item in the `Dict`.
+([PR #2701](https://github.com/modularml/mojo/pull/2701)
+by [@jayzhan211](https://github.com/jayzhan211))
+
 - Add a `sort` function for list of `ComparableCollectionElement`s.
   [PR #2609](https://github.com/modularml/mojo/pull/2609) by
   [@mzaks](https://github.com/mzaks)

stdlib/src/collections/dict.mojo

@@ -799,6 +799,34 @@ struct Dict[K: KeyElement, V: CollectionElement](
             return default.value()[]
         raise "KeyError"
 
+    fn popitem(inout self) raises -> DictEntry[K, V]:
+        """Remove and return a (key, value) pair from the dictionary. Pairs are returned in LIFO order.
+        popitem() is useful to destructively iterate over a dictionary, as often used in set algorithms.
+        If the dictionary is empty, calling popitem() raises a KeyError.
+
+        Args: None
+
+        Returns:
+            Last dictionary item
+
+        Raises:
+            "KeyError" if the dictionary is empty.
+        """
+
+        var key = Optional[K](None)
+        var val = Optional[V](None)
+
+        for item in reversed(self.items()):
+            key = Optional(item[].key)
+            val = Optional(item[].value)
+            break
+
+        if key:
+            _ = self.pop(key.value()[])
+            return DictEntry[K, V](key.value()[], val.value()[])
+
+        raise "KeyError: popitem(): dictionary is empty"
+
     fn keys(
         self: Reference[Self, _, _]
     ) -> _DictKeyIter[K, V, self.is_mutable, self.lifetime]:

stdlib/test/collections/test_dict.mojo

@@ -452,6 +452,7 @@ def test_dict():
     test["test_dict_update_empty_new", test_dict_update_empty_new]()
     test["test_mojo_issue_1729", test_mojo_issue_1729]()
     test["test dict or", test_dict_or]()
+    test["test dict popteim", test_dict_popitem]()
 
 
 def test_taking_owned_kwargs_dict(owned kwargs: OwnedKwargsDict[Int]):
@@ -512,6 +513,21 @@ def test_find_get():
     assert_equal(some_dict.get("not_key", 0), 0)
 
 
+def test_dict_popitem():
+    var dict = Dict[String, Int]()
+    dict["a"] = 1
+    dict["b"] = 2
+
+    var item = dict.popitem()
+    assert_equal(item.key, "b")
+    assert_equal(item.value, 2)
+    item = dict.popitem()
+    assert_equal(item.key, "a")
+    assert_equal(item.value, 1)
+    with assert_raises(contains="KeyError"):
+        _ = dict.popitem()
+
+
 fn test_clear() raises:
     var some_dict = Dict[String, Int]()
     some_dict["key"] = 1