Propose a getitem() method

pep-0455.txt

@@ -95,6 +95,23 @@ constructors::
    >>> sorted(d.items())
    [('Bar', 2), ('Foo', 1)]
 
+Getting the original key
+------------------------
+
+TransformDict also features a lookup method returning the stored key
+together with the corresponding value::
+
+    >>> d = TransformDict(str.casefold, {'Foo': 1})
+    >>> d.getitem('FOO')
+    ('Foo', 1)
+    >>> d.getitem('bar')
+    Traceback (most recent call last):
+      File "<stdin>", line 1, in <module>
+    KeyError: 'bar'
+
+The method name ``getitem()`` mirrors the standard ``popitem()`` method
+on mutable mappings.
+
 
 Alternative proposals and questions
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