PEP 845: Add clarification and rejected idea (GH-5143)

Author: cdce8p

peps/pep-0845.rst

@@ -1,6 +1,7 @@
 PEP: 845
 Title: Leading-Dot Value Patterns
-Author: Thomas Kehrenberg <tmke8@posteo.net>, Marc Mueller
+Author: Thomas Kehrenberg <tmke8@posteo.net>,
+        Marc Mueller
 Sponsor: Ethan Furman <ethan@stoneleaf.us>
 Discussions-To: https://discuss.python.org/t/pep-845-leading-dot-value-patterns/109100
 Status: Draft
@@ -120,6 +121,25 @@ The value pattern will be extended to support simple names
 if they are prefixed by a leading dot. The lookup is performed following the
 standard Python name resolution rules.
 
+Interaction with capture patterns
+---------------------------------
+
+**Capture patterns** are only assigned **after** a case matches but
+before the guard clause is evaluated. Any lookup will resolve to an
+existing variable if one exists, or raise an error.
+
+.. code-block:: python-console
+
+    >>> match [1, 1]:
+    ...     case [x, *_, .x]:
+    ...        pass
+    ...
+    Traceback (most recent call last):
+    File "<python-input-0>", line 2, in <module>
+        case [x, *_, .x]:
+                      ^
+    NameError: name 'x' is not defined
+
 Grammar
 -------
 
@@ -288,6 +308,18 @@ Standard name resolution covers all of these scopes without additional syntax.
 In addition, ``nonlocal.NAME`` does not have an equivalent expression form
 elsewhere in Python.
 
+Reuse existing typing constructs (``Literal[NAME]``)
+----------------------------------------------------
+
+It was suggested to reuse ``Literal`` from :py:class:`typing.Literal` to
+match simple names. So far no names other than ``_`` have a dedicated meaning
+in the match statement mini-syntax. Assigning one to ``Literal`` would
+thus be surprising. Additionally, subscription is not defined for use in
+match cases yet. Using it here would limit future options unnecessarily.
+Lastly, :py:class:`typing.Literal` only supports literal values as arguments,
+e.g. ``1``, ``"Hello"`` or ``True``. Allowing simple names only inside
+match cases would therefore be confusing.
+
 Distinguishing by case of the name
 ----------------------------------
 
@@ -355,6 +387,15 @@ Note the difference from the class pattern ``case int():``, which matches
 object itself.
 
 
+Change History
+==============
+
+* 25-Sep-2026
+
+  - Clarify interaction with **capture patterns**
+  - Added rejected idea for ``Literal[NAME]``
+
+
 Copyright
 =========