[Python-checkins] bpo-32892: Support subclasses of base types in isinstance checks for AST constants. (GH-9934)

[Serhiy Storchaka]

https://github.com/python/cpython/commit/6015cc50bc38b9e920ce4986ee10658eaa14f561
commit: 6015cc50bc38b9e920ce4986ee10658eaa14f561
branch: master
author: Serhiy Storchaka <storchaka at gmail.com>
committer: GitHub <noreply at github.com>
date: 2018-10-28T13:43:03+02:00
summary:

bpo-32892: Support subclasses of base types in isinstance checks for AST constants. (GH-9934)

Some projects (e.g. Chameleon) create ast.Str containing an instance
of the str subclass.

files:
M Lib/ast.py
M Lib/test/test_ast.py

diff --git a/Lib/ast.py b/Lib/ast.py
index de3df1473e5e..4c8c7795ff82 100644
--- a/Lib/ast.py
+++ b/Lib/ast.py
@@ -346,7 +346,7 @@ def __instancecheck__(cls, inst):
             except AttributeError:
                 return False
             else:
-                return type(value) in _const_types[cls]
+                return isinstance(value, _const_types[cls])
         return type.__instancecheck__(cls, inst)
 
 def _new(cls, *args, **kwargs):
diff --git a/Lib/test/test_ast.py b/Lib/test/test_ast.py
index 10be02eee0c0..4bbdc3b82daa 100644
--- a/Lib/test/test_ast.py
+++ b/Lib/test/test_ast.py
@@ -399,6 +399,10 @@ def test_isinstance(self):
         self.assertFalse(isinstance(ast.Constant(), ast.NameConstant))
         self.assertFalse(isinstance(ast.Constant(), ast.Ellipsis))
 
+        class S(str): pass
+        self.assertTrue(isinstance(ast.Constant(S('42')), ast.Str))
+        self.assertFalse(isinstance(ast.Constant(S('42')), ast.Num))
+
     def test_subclasses(self):
         class N(ast.Num):
             def __init__(self, *args, **kwargs):