bpo-35975: Support parsing earlier minor versions of Python 3 (GH-12086)

This adds a `feature_version` flag to `ast.parse()` (documented) and `compile()` (hidden) that allow tweaking the parser to support older versions of the grammar. In particular if `feature_version` is 5 or 6, the hacks for the `async` and `await` keyword from PEP 492 are reinstated. (For 7 or higher, these are unconditionally treated as keywords, but they are still special tokens rather than `NAME` tokens that the parser driver recognizes.)



https://bugs.python.org/issue35975

1 files changed, 4 insertions, 2 deletions

diff --git a/Lib/ast.py b/Lib/ast.py
index 470a74b..64e7a25 100644
--- a/Lib/ast.py
+++ b/Lib/ast.py
@@ -27,7 +27,8 @@
 from _ast import *
 
 
-def parse(source, filename='<unknown>', mode='exec', *, type_comments=False):
+def parse(source, filename='<unknown>', mode='exec', *,
+          type_comments=False, feature_version=-1):
     """
     Parse the source into an AST node.
     Equivalent to compile(source, filename, mode, PyCF_ONLY_AST).
@@ -36,7 +37,8 @@ def parse(source, filename='<unknown>', mode='exec', *, type_comments=False):
     flags = PyCF_ONLY_AST
     if type_comments:
         flags |= PyCF_TYPE_COMMENTS
-    return compile(source, filename, mode, flags)
+    return compile(source, filename, mode, flags,
+                   feature_version=feature_version)
 
 
 def literal_eval(node_or_string):