[stdlib] Implement Dict.popitem() method

docs/changelog.md

@@ -18,6 +18,11 @@ what we publish.
 
 ### ⭐️ New
 
+- `Dict` now supports `popitem`, which removes and returns the last item in the `Dict`.
+  The item is returned as a (key, value) pair.
+  ([PR #2794](https://github.com/modularml/mojo/pull/2794)
+  by [@msaelices](https://github.com/msaelices)) and [@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 +799,23 @@ struct Dict[K: KeyElement, V: CollectionElement](
             return default.value()[]
         raise "KeyError"
 
+    fn popitem(inout self) raises -> (K, V):
+        """Remove and return an arbitrary key-value pair from the dictionary.
+
+        Returns:
+            A tuple containing the key and value of the removed item.
+
+        Raises:
+            "KeyError" if the dictionary is empty.
+        """
+        if self.size == 0:
+            raise "KeyError: popitem(): dictionary is empty"
+        var reversed_items = reversed(self.items())
+        var entry_ref = reversed_items.__next__()  # TODO: Use next() when supported in Mojo
+        var entry = entry_ref[]
+        _ = self.pop(entry.key)
+        return (entry.key, entry.value)
+
     fn keys(
         self: Reference[Self, _, _]
     ) -> _DictKeyIter[K, V, self.is_mutable, self.lifetime]:

stdlib/test/collections/test_dict.mojo

@@ -152,6 +152,32 @@ def test_pop_default():
     assert_equal(-1, dict.pop("c", -1))
 
 
+def test_popitem():
+    var dict = Dict[String, Int]()
+    dict["a"] = 1
+    dict["b"] = 2
+
+    var t1: (String, Int) = dict.popitem()
+    assert_equal(t1[0], "b")
+    assert_equal(t1[1], 2)
+    assert_equal(1, len(dict))
+
+    dict["c"] = 3
+
+    var t2: (String, Int) = dict.popitem()
+    assert_equal(t2[0], "c")
+    assert_equal(t2[1], 3)
+    assert_equal(1, len(dict))
+
+    var t3: (String, Int) = dict.popitem()
+    assert_equal(t3[0], "a")
+    assert_equal(t3[1], 1)
+    assert_equal(0, len(dict))
+
+    with assert_raises(contains="KeyError"):
+        _ = dict.popitem()
+
+
 def test_key_error():
     var dict = Dict[String, Int]()
 
@@ -434,6 +460,7 @@ def test_dict():
     test["test_compact", test_compact]()
     test["test_compact_with_elements", test_compact_with_elements]()
     test["test_pop_default", test_pop_default]()
+    test["test_popitem", test_popitem]()
     test["test_key_error", test_key_error]()
     test["test_iter", test_iter]()
     test["test_iter_keys", test_iter_keys]()