Add ast.Constant

Issue #26146: Add a new kind of AST node: ast.Constant. It can be used by
external AST optimizers, but the compiler does not emit directly such node.

An optimizer can replace the following AST nodes with ast.Constant:

* ast.NameConstant: None, False, True
* ast.Num: int, float, complex
* ast.Str: str
* ast.Bytes: bytes
* ast.Tuple if items are constants too: tuple
* frozenset

Update code to accept ast.Constant instead of ast.Num and/or ast.Str:

* compiler
* docstrings
* ast.literal_eval()
* Tools/parser/unparse.py

1 files changed, 4 insertions, 1 deletions

diff --git a/Python/future.c b/Python/future.c
index 163f87f..75f2107 100644
--- a/Python/future.c
+++ b/Python/future.c
@@ -79,7 +79,10 @@ future_parse(PyFutureFeatures *ff, mod_ty mod, PyObject *filename)
 
     i = 0;
     first = (stmt_ty)asdl_seq_GET(mod->v.Module.body, i);
-    if (first->kind == Expr_kind && first->v.Expr.value->kind == Str_kind)
+    if (first->kind == Expr_kind
+        && (first->v.Expr.value->kind == Str_kind
+            || (first->v.Expr.value->kind == Constant_kind
+                && PyUnicode_CheckExact(first->v.Expr.value->v.Constant.value))))
         i++;