gh-131421: fix ASDL grammar for `Dict` to have an `expr?*` keys field (#131419)

In the `ast` documentation for Python:

* https://docs.python.org/3/library/ast.html#ast.Dict
it is made clear that:

> When doing dictionary unpacking using dictionary literals the expression to be expanded goes in the values list, with a `None` at the corresponding position in `keys`.

Hence, `keys` is really a `expr?*` and *not* a `expr*`.

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/Python/Python-ast.c b/Python/Python-ast.c
index 94d9a76..df03556 100644
--- a/Python/Python-ast.c
+++ b/Python/Python-ast.c
@@ -6362,7 +6362,7 @@ init_types(void *arg)
         "     | UnaryOp(unaryop op, expr operand)\n"
         "     | Lambda(arguments args, expr body)\n"
         "     | IfExp(expr test, expr body, expr orelse)\n"
-        "     | Dict(expr* keys, expr* values)\n"
+        "     | Dict(expr?* keys, expr* values)\n"
         "     | Set(expr* elts)\n"
         "     | ListComp(expr elt, comprehension* generators)\n"
         "     | SetComp(expr elt, comprehension* generators)\n"
@@ -6419,7 +6419,7 @@ init_types(void *arg)
     if (!state->IfExp_type) return -1;
     state->Dict_type = make_type(state, "Dict", state->expr_type, Dict_fields,
                                  2,
-        "Dict(expr* keys, expr* values)");
+        "Dict(expr?* keys, expr* values)");
     if (!state->Dict_type) return -1;
     state->Set_type = make_type(state, "Set", state->expr_type, Set_fields, 1,
         "Set(expr* elts)");