bpo-39999: Improve compatibility of the ast module. (GH-19056)

* Re-add removed classes Suite, slice, Param, AugLoad and AugStore.
* Add docstrings for dummy classes.
* Add docstrings for attribute aliases.
* Set __module__ to "ast" instead of "_ast".

2 files changed, 26 insertions, 4 deletions

diff --git a/Lib/ast.py b/Lib/ast.py
index e347d8b..f51c71f 100644
--- a/Lib/ast.py
+++ b/Lib/ast.py
@@ -489,6 +489,7 @@ class NodeTransformer(NodeVisitor):
 # It will be removed in future.
 
 def _getter(self):
+    """Deprecated. Use value instead."""
     return self.value
 
 def _setter(self, value):
@@ -499,6 +500,9 @@ Constant.s = property(_getter, _setter)
 
 class _ABC(type):
 
+    def __init__(cls, *args):
+        cls.__doc__ = """Deprecated AST node class. Use ast.Constant instead"""
+
     def __instancecheck__(cls, inst):
         if not isinstance(inst, Constant):
             return False
@@ -564,15 +568,21 @@ _const_node_type_names = {
     type(...): 'Ellipsis',
 }
 
-class Index(AST):
+class slice(AST):
+    """Deprecated AST node class."""
+
+class Index(slice):
+    """Deprecated AST node class. Use the index value directly instead."""
     def __new__(cls, value, **kwargs):
         return value
 
-class ExtSlice(AST):
+class ExtSlice(slice):
+    """Deprecated AST node class. Use ast.Tuple instead."""
     def __new__(cls, dims=(), **kwargs):
         return Tuple(list(dims), Load(), **kwargs)
 
 def _dims_getter(self):
+    """Deprecated. Use elts instead."""
     return self.elts
 
 def _dims_setter(self, value):
@@ -580,6 +590,18 @@ def _dims_setter(self, value):
 
 Tuple.dims = property(_dims_getter, _dims_setter)
 
+class Suite(mod):
+    """Deprecated AST node class.  Unused in Python 3."""
+
+class AugLoad(expr_context):
+    """Deprecated AST node class.  Unused in Python 3."""
+
+class AugStore(expr_context):
+    """Deprecated AST node class.  Unused in Python 3."""
+
+class Param(expr_context):
+    """Deprecated AST node class.  Unused in Python 3."""
+
 
 # Large float and imaginary literals get turned into infinities in the AST.
 # We unparse those infinities to INFSTR.
diff --git a/Lib/test/test_ast.py b/Lib/test/test_ast.py
index d072c33..3fd982c 100644
--- a/Lib/test/test_ast.py
+++ b/Lib/test/test_ast.py
@@ -283,7 +283,7 @@ class AST_Tests(unittest.TestCase):
             x.vararg
 
         with self.assertRaises(TypeError):
-            # "_ast.AST constructor takes 0 positional arguments"
+            # "ast.AST constructor takes 0 positional arguments"
             ast.AST(2)
 
     def test_AST_garbage_collection(self):
@@ -573,7 +573,7 @@ class AST_Tests(unittest.TestCase):
         m = ast.Module([ast.Expr(ast.expr(**pos), **pos)], [])
         with self.assertRaises(TypeError) as cm:
             compile(m, "<test>", "exec")
-        self.assertIn("but got <_ast.expr", str(cm.exception))
+        self.assertIn("but got <ast.expr", str(cm.exception))
 
     def test_invalid_identifier(self):
         m = ast.Module([ast.Expr(ast.Name(42, ast.Load()))], [])