From c3ea41e9bf100a5396b851488c3efe208e5e2179 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Mon, 26 Aug 2019 10:13:19 +0300
Subject: bpo-36917: Add default implementation of
 ast.NodeVisitor.visit_Constant(). (GH-15490)

It emits a deprecation warning and calls corresponding method
visit_Num(), visit_Str(), etc.
---
 Lib/ast.py | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

(limited to 'Lib/ast.py')

diff --git a/Lib/ast.py b/Lib/ast.py
index ffeba179e5..1e639d11fe 100644
--- a/Lib/ast.py
+++ b/Lib/ast.py
@@ -360,6 +360,27 @@ class NodeVisitor(object):
             elif isinstance(value, AST):
                 self.visit(value)
 
+    def visit_Constant(self, node):
+        value = node.value
+        type_name = _const_node_type_names.get(type(value))
+        if type_name is None:
+            for cls, name in _const_node_type_names.items():
+                if isinstance(value, cls):
+                    type_name = name
+                    break
+        if type_name is not None:
+            method = 'visit_' + type_name
+            try:
+                visitor = getattr(self, method)
+            except AttributeError:
+                pass
+            else:
+                import warnings
+                warnings.warn(f"{method} is deprecated; add visit_Constant",
+                              DeprecationWarning, 2)
+                return visitor(node)
+        return self.generic_visit(node)
+
 
 class NodeTransformer(NodeVisitor):
     """
@@ -487,3 +508,13 @@ _const_types = {
 _const_types_not = {
     Num: (bool,),
 }
+_const_node_type_names = {
+    bool: 'NameConstant',  # should be before int
+    type(None): 'NameConstant',
+    int: 'Num',
+    float: 'Num',
+    complex: 'Num',
+    str: 'Str',
+    bytes: 'Bytes',
+    type(...): 'Ellipsis',
+}
-- 
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