Work towards feature_version support
Visible behavior: - Issue error for `X @ Y` (matrix multiply) if c_feature_version < 5 - Add optional feature_version kw arg to ast.parse() (default -1 which implies PY_MINOR_VERSION) - Add feature_version: int = -1 to compile() (via Argument Clinic); this sets cf_feature_version to the given value if >= 0, else defaults to PY_MINOR_VERSION Implementation: - Add PyAST_obj2mod_ex(): like PyAST_obj2mod() but with feature_version arg; the latter calls the former with PY_MINOR_VERSION - Add cf_feature_version to PyCompilerFlags structure; initialized to PY_MINOR_VERSION everywhere - Add c_feature_version to struct compiling; initialize from cf_feature_version - Add 'c' argument to get_operator() - In builtin eval() and exec(), default to PY_MINOR_VERSION TODO: - Put version-dependent ASYNC/AWAIT keyword scanning back - Reject async functions, await expressions, and async for/with in minor versions < 5 - Reject async comprehensions in minor versions < 6 - Reject underscores in numeric literals in minor versions < 6 - Reject variable annotations in minor versions < 6 - Reject `X @= Y` in minor versions < 5

Visible behavior: - Issue error for `X @ Y` (matrix multiply) if c_feature_version < 5 - Add optional feature_version kw arg to ast.parse() (default -1 which implies PY_MINOR_VERSION) - Add feature_version: int = -1 to compile() (via Argument Clinic); this sets cf_feature_version to the given value if >= 0, else defaults to PY_MINOR_VERSION Implementation: - Add PyAST_obj2mod_ex(): like PyAST_obj2mod() but with feature_version arg; the latter calls the former with PY_MINOR_VERSION - Add cf_feature_version to PyCompilerFlags structure; initialized to PY_MINOR_VERSION everywhere - Add c_feature_version to struct compiling; initialize from cf_feature_version - Add 'c' argument to get_operator() - In builtin eval() and exec(), default to PY_MINOR_VERSION TODO: - Put version-dependent ASYNC/AWAIT keyword scanning back - Reject async functions, await expressions, and async for/with in minor versions < 5 - Reject async comprehensions in minor versions < 6 - Reject underscores in numeric literals in minor versions < 6 - Reject variable annotations in minor versions < 6 - Reject `X @= Y` in minor versions < 5
Implement further restrictions on feature_version
This is everything currently in typeshed except await expressions (but it does reject async functions etc.): - Reject async functions and async for/with in minor versions < 5 - Reject async comprehensions in minor versions < 6 - Reject underscores in numeric literals in minor versions < 6 - Reject variable annotations in minor versions < 6 - Reject `X @= Y` in minor versions < 5
python · miss-islington · Mar 7, 2019 · miss-islington · Mar 7, 2019 · gvanrossum
diff --git a/Lib/ast.py b/Lib/ast.py
-    return compile(source, filename, mode, flags)
+    return compile(source, filename, mode, flags,
+                   dont_inherit=False,
+                   optimize=-1,
diff --git a/Python/ast.c b/Python/ast.c
+        /* Async comprehensions only allowed in Python 3.6 and greater */
+        if (is_async && c->c_feature_version < 6) {
+            ast_error(c, n,
+                    "Async comprehensions are only supported in Python 3.6 and greater");
diff --git a/Python/ast.c b/Python/ast.c
@@ -1746,6 +1758,12 @@ ast_for_funcdef_impl(struct compiling *c, const node *n0,
    node *tc;
    string type_comment = NULL;

+    if (is_async && c->c_feature_version < 5) {
+        ast_error(c, n,
+                  "Async functions are only supported in Python 3.5 and greater");
diff --git a/Doc/library/ast.rst b/Doc/library/ast.rst
@@ -145,13 +145,18 @@ and classes for traversing abstract syntax trees:
   modified to correspond to :pep:`484` "signature type comments",
   e.g. ``(str, int) -> List[str]``.

+   Also, setting ``feature_version`` to the minor version of an
+   earlier Python 3 version will attempt to parse using that version's
+   grammar.  For example, setting ``feature_version=4`` will allow
diff --git a/Lib/test/test_type_comments.py b/Lib/test/test_type_comments.py
+        return ast.parse(source, type_comments=True,
+                         feature_version=feature_version)
+
+    def parses(self, source, minver=lowest, maxver=highest, expected_regex=""):
diff --git a/Lib/test/test_type_comments.py b/Lib/test/test_type_comments.py
+fstring = """\
+a = 42
+f"{a}"
+"""