bpo-36280: Add Constant.kind field (GH-12295)

The value is a string for string and byte literals, None otherwise.
It is 'u' for u"..." literals, 'b' for b"..." literals, '' for "..." literals.
The 'r' (raw) prefix is ignored.
Does not apply to f-strings.

This appears sufficient to make mypy capable of using the stdlib ast module instead of typed_ast (assuming a mypy patch I'm working on).

WIP: I need to make the tests pass. @ilevkivskyi @serhiy-storchaka 



https://bugs.python.org/issue36280

6 files changed, 142 insertions, 60 deletions

diff --git a/Include/Python-ast.h b/Include/Python-ast.h
index 8265bed8d6..a5742ff048 100644
--- a/Include/Python-ast.h
+++ b/Include/Python-ast.h
@@ -338,6 +338,7 @@ struct _expr {
 
         struct {
             constant value;
+            string kind;
         } Constant;
 
         struct {
@@ -642,9 +643,9 @@ expr_ty _Py_FormattedValue(expr_ty value, int conversion, expr_ty format_spec,
 #define JoinedStr(a0, a1, a2, a3, a4, a5) _Py_JoinedStr(a0, a1, a2, a3, a4, a5)
 expr_ty _Py_JoinedStr(asdl_seq * values, int lineno, int col_offset, int
                       end_lineno, int end_col_offset, PyArena *arena);
-#define Constant(a0, a1, a2, a3, a4, a5) _Py_Constant(a0, a1, a2, a3, a4, a5)
-expr_ty _Py_Constant(constant value, int lineno, int col_offset, int
-                     end_lineno, int end_col_offset, PyArena *arena);
+#define Constant(a0, a1, a2, a3, a4, a5, a6) _Py_Constant(a0, a1, a2, a3, a4, a5, a6)
+expr_ty _Py_Constant(constant value, string kind, int lineno, int col_offset,
+                     int end_lineno, int end_col_offset, PyArena *arena);
 #define Attribute(a0, a1, a2, a3, a4, a5, a6, a7) _Py_Attribute(a0, a1, a2, a3, a4, a5, a6, a7)
 expr_ty _Py_Attribute(expr_ty value, identifier attr, expr_context_ty ctx, int
                       lineno, int col_offset, int end_lineno, int
diff --git a/Lib/test/test_ast.py b/Lib/test/test_ast.py
index 609c8b2c6a..a7ee0da38d 100644
--- a/Lib/test/test_ast.py
+++ b/Lib/test/test_ast.py
@@ -326,7 +326,7 @@ class AST_Tests(unittest.TestCase):
 
     def test_classattrs(self):
         x = ast.Num()
-        self.assertEqual(x._fields, ('value',))
+        self.assertEqual(x._fields, ('value', 'kind'))
 
         with self.assertRaises(AttributeError):
             x.value
@@ -349,12 +349,12 @@ class AST_Tests(unittest.TestCase):
 
         x = ast.Num(42, lineno=0)
         self.assertEqual(x.lineno, 0)
-        self.assertEqual(x._fields, ('value',))
+        self.assertEqual(x._fields, ('value', 'kind'))
         self.assertEqual(x.value, 42)
         self.assertEqual(x.n, 42)
 
-        self.assertRaises(TypeError, ast.Num, 1, 2)
-        self.assertRaises(TypeError, ast.Num, 1, 2, lineno=0)
+        self.assertRaises(TypeError, ast.Num, 1, None, 2)
+        self.assertRaises(TypeError, ast.Num, 1, None, 2, lineno=0)
 
         self.assertEqual(ast.Num(42).n, 42)
         self.assertEqual(ast.Num(4.25).n, 4.25)
@@ -556,6 +556,7 @@ class AST_Tests(unittest.TestCase):
 
 
 class ASTHelpers_Test(unittest.TestCase):
+    maxDiff = None
 
     def test_parse(self):
         a = ast.parse('foo(1 + 1)')
@@ -574,18 +575,18 @@ class ASTHelpers_Test(unittest.TestCase):
         node = ast.parse('spam(eggs, "and cheese")')
         self.assertEqual(ast.dump(node),
             "Module(body=[Expr(value=Call(func=Name(id='spam', ctx=Load()), "
-            "args=[Name(id='eggs', ctx=Load()), Constant(value='and cheese')], "
+            "args=[Name(id='eggs', ctx=Load()), Constant(value='and cheese', kind=None)], "
             "keywords=[]))], type_ignores=[])"
         )
         self.assertEqual(ast.dump(node, annotate_fields=False),
             "Module([Expr(Call(Name('spam', Load()), [Name('eggs', Load()), "
-            "Constant('and cheese')], []))], [])"
+            "Constant('and cheese', None)], []))], [])"
         )
         self.assertEqual(ast.dump(node, include_attributes=True),
             "Module(body=[Expr(value=Call(func=Name(id='spam', ctx=Load(), "
             "lineno=1, col_offset=0, end_lineno=1, end_col_offset=4), "
             "args=[Name(id='eggs', ctx=Load(), lineno=1, col_offset=5, "
-            "end_lineno=1, end_col_offset=9), Constant(value='and cheese', "
+            "end_lineno=1, end_col_offset=9), Constant(value='and cheese', kind=None, "
             "lineno=1, col_offset=11, end_lineno=1, end_col_offset=23)], keywords=[], "
             "lineno=1, col_offset=0, end_lineno=1, end_col_offset=24), "
             "lineno=1, col_offset=0, end_lineno=1, end_col_offset=24)], type_ignores=[])"
@@ -595,7 +596,7 @@ class ASTHelpers_Test(unittest.TestCase):
         src = ast.parse('1 + 1', mode='eval')
         src.body.right = ast.copy_location(ast.Num(2), src.body.right)
         self.assertEqual(ast.dump(src, include_attributes=True),
-            'Expression(body=BinOp(left=Constant(value=1, lineno=1, col_offset=0, '
+            'Expression(body=BinOp(left=Constant(value=1, kind=None, lineno=1, col_offset=0, '
             'end_lineno=1, end_col_offset=1), op=Add(), right=Constant(value=2, '
             'lineno=1, col_offset=4, end_lineno=1, end_col_offset=5), lineno=1, '
             'col_offset=0, end_lineno=1, end_col_offset=5))'
@@ -610,7 +611,7 @@ class ASTHelpers_Test(unittest.TestCase):
         self.assertEqual(ast.dump(src, include_attributes=True),
             "Module(body=[Expr(value=Call(func=Name(id='write', ctx=Load(), "
             "lineno=1, col_offset=0, end_lineno=1, end_col_offset=5), "
-            "args=[Constant(value='spam', lineno=1, col_offset=6, end_lineno=1, "
+            "args=[Constant(value='spam', kind=None, lineno=1, col_offset=6, end_lineno=1, "
             "end_col_offset=12)], keywords=[], lineno=1, col_offset=0, end_lineno=1, "
             "end_col_offset=13), lineno=1, col_offset=0, end_lineno=1, "
             "end_col_offset=13), Expr(value=Call(func=Name(id='spam', ctx=Load(), "
@@ -625,8 +626,8 @@ class ASTHelpers_Test(unittest.TestCase):
         src = ast.parse('1 + 1', mode='eval')
         self.assertEqual(ast.increment_lineno(src, n=3), src)
         self.assertEqual(ast.dump(src, include_attributes=True),
-            'Expression(body=BinOp(left=Constant(value=1, lineno=4, col_offset=0, '
-            'end_lineno=4, end_col_offset=1), op=Add(), right=Constant(value=1, '
+            'Expression(body=BinOp(left=Constant(value=1, kind=None, lineno=4, col_offset=0, '
+            'end_lineno=4, end_col_offset=1), op=Add(), right=Constant(value=1, kind=None, '
             'lineno=4, col_offset=4, end_lineno=4, end_col_offset=5), lineno=4, '
             'col_offset=0, end_lineno=4, end_col_offset=5))'
         )
@@ -634,8 +635,8 @@ class ASTHelpers_Test(unittest.TestCase):
         src = ast.parse('1 + 1', mode='eval')
         self.assertEqual(ast.increment_lineno(src.body, n=3), src.body)
         self.assertEqual(ast.dump(src, include_attributes=True),
-            'Expression(body=BinOp(left=Constant(value=1, lineno=4, col_offset=0, '
-            'end_lineno=4, end_col_offset=1), op=Add(), right=Constant(value=1, '
+            'Expression(body=BinOp(left=Constant(value=1, kind=None, lineno=4, col_offset=0, '
+            'end_lineno=4, end_col_offset=1), op=Add(), right=Constant(value=1, kind=None, '
             'lineno=4, col_offset=4, end_lineno=4, end_col_offset=5), lineno=4, '
             'col_offset=0, end_lineno=4, end_col_offset=5))'
         )
@@ -654,7 +655,7 @@ class ASTHelpers_Test(unittest.TestCase):
         self.assertEqual(next(iterator).value, 23)
         self.assertEqual(next(iterator).value, 42)
         self.assertEqual(ast.dump(next(iterator)),
-            "keyword(arg='eggs', value=Constant(value='leek'))"
+            "keyword(arg='eggs', value=Constant(value='leek', kind=None))"
         )
 
     def test_get_docstring(self):
@@ -1283,6 +1284,23 @@ class ConstantTests(unittest.TestCase):
 
         self.assertEqual(ast.literal_eval(binop), 10+20j)
 
+    def test_string_kind(self):
+        c = ast.parse('"x"', mode='eval').body
+        self.assertEqual(c.value, "x")
+        self.assertEqual(c.kind, None)
+
+        c = ast.parse('u"x"', mode='eval').body
+        self.assertEqual(c.value, "x")
+        self.assertEqual(c.kind, "u")
+
+        c = ast.parse('r"x"', mode='eval').body
+        self.assertEqual(c.value, "x")
+        self.assertEqual(c.kind, None)
+
+        c = ast.parse('b"x"', mode='eval').body
+        self.assertEqual(c.value, b"x")
+        self.assertEqual(c.kind, None)
+
 
 class EndPositionTests(unittest.TestCase):
     """Tests for end position of AST nodes.
@@ -1606,38 +1624,38 @@ def main():
 
 #### EVERYTHING BELOW IS GENERATED BY python Lib/test/test_ast.py -g  #####
 exec_results = [
-('Module', [('Expr', (1, 0), ('Constant', (1, 0), None))], []),
-('Module', [('Expr', (1, 0), ('Constant', (1, 0), 'module docstring'))], []),
+('Module', [('Expr', (1, 0), ('Constant', (1, 0), None, None))], []),
+('Module', [('Expr', (1, 0), ('Constant', (1, 0), 'module docstring', None))], []),
 ('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('Pass', (1, 9))], [], None, None)], []),
-('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('Expr', (1, 9), ('Constant', (1, 9), 'function docstring'))], [], None, None)], []),
+('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('Expr', (1, 9), ('Constant', (1, 9), 'function docstring', None))], [], None, None)], []),
 ('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [('arg', (1, 6), 'a', None, None)], None, [], [], None, []), [('Pass', (1, 10))], [], None, None)], []),
-('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [('arg', (1, 6), 'a', None, None)], None, [], [], None, [('Constant', (1, 8), 0)]), [('Pass', (1, 12))], [], None, None)], []),
+('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [('arg', (1, 6), 'a', None, None)], None, [], [], None, [('Constant', (1, 8), 0, None)]), [('Pass', (1, 12))], [], None, None)], []),
 ('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [], ('arg', (1, 7), 'args', None, None), [], [], None, []), [('Pass', (1, 14))], [], None, None)], []),
 ('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], ('arg', (1, 8), 'kwargs', None, None), []), [('Pass', (1, 17))], [], None, None)], []),
-('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [('arg', (1, 6), 'a', None, None), ('arg', (1, 9), 'b', None, None), ('arg', (1, 14), 'c', None, None), ('arg', (1, 22), 'd', None, None), ('arg', (1, 28), 'e', None, None)], ('arg', (1, 35), 'args', None, None), [('arg', (1, 41), 'f', None, None)], [('Constant', (1, 43), 42)], ('arg', (1, 49), 'kwargs', None, None), [('Constant', (1, 11), 1), ('Constant', (1, 16), None), ('List', (1, 24), [], ('Load',)), ('Dict', (1, 30), [], [])]), [('Expr', (1, 58), ('Constant', (1, 58), 'doc for f()'))], [], None, None)], []),
+('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [('arg', (1, 6), 'a', None, None), ('arg', (1, 9), 'b', None, None), ('arg', (1, 14), 'c', None, None), ('arg', (1, 22), 'd', None, None), ('arg', (1, 28), 'e', None, None)], ('arg', (1, 35), 'args', None, None), [('arg', (1, 41), 'f', None, None)], [('Constant', (1, 43), 42, None)], ('arg', (1, 49), 'kwargs', None, None), [('Constant', (1, 11), 1, None), ('Constant', (1, 16), None, None), ('List', (1, 24), [], ('Load',)), ('Dict', (1, 30), [], [])]), [('Expr', (1, 58), ('Constant', (1, 58), 'doc for f()', None))], [], None, None)], []),
 ('Module', [('ClassDef', (1, 0), 'C', [], [], [('Pass', (1, 8))], [])], []),
-('Module', [('ClassDef', (1, 0), 'C', [], [], [('Expr', (1, 9), ('Constant', (1, 9), 'docstring for class C'))], [])], []),
+('Module', [('ClassDef', (1, 0), 'C', [], [], [('Expr', (1, 9), ('Constant', (1, 9), 'docstring for class C', None))], [])], []),
 ('Module', [('ClassDef', (1, 0), 'C', [('Name', (1, 8), 'object', ('Load',))], [], [('Pass', (1, 17))], [])], []),
-('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('Return', (1, 8), ('Constant', (1, 15), 1))], [], None, None)], []),
+('Module', [('FunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('Return', (1, 8), ('Constant', (1, 15), 1, None))], [], None, None)], []),
 ('Module', [('Delete', (1, 0), [('Name', (1, 4), 'v', ('Del',))])], []),
-('Module', [('Assign', (1, 0), [('Name', (1, 0), 'v', ('Store',))], ('Constant', (1, 4), 1), None)], []),
+('Module', [('Assign', (1, 0), [('Name', (1, 0), 'v', ('Store',))], ('Constant', (1, 4), 1, None), None)], []),
 ('Module', [('Assign', (1, 0), [('Tuple', (1, 0), [('Name', (1, 0), 'a', ('Store',)), ('Name', (1, 2), 'b', ('Store',))], ('Store',))], ('Name', (1, 6), 'c', ('Load',)), None)], []),
 ('Module', [('Assign', (1, 0), [('Tuple', (1, 0), [('Name', (1, 1), 'a', ('Store',)), ('Name', (1, 3), 'b', ('Store',))], ('Store',))], ('Name', (1, 8), 'c', ('Load',)), None)], []),
 ('Module', [('Assign', (1, 0), [('List', (1, 0), [('Name', (1, 1), 'a', ('Store',)), ('Name', (1, 3), 'b', ('Store',))], ('Store',))], ('Name', (1, 8), 'c', ('Load',)), None)], []),
-('Module', [('AugAssign', (1, 0), ('Name', (1, 0), 'v', ('Store',)), ('Add',), ('Constant', (1, 5), 1))], []),
+('Module', [('AugAssign', (1, 0), ('Name', (1, 0), 'v', ('Store',)), ('Add',), ('Constant', (1, 5), 1, None))], []),
 ('Module', [('For', (1, 0), ('Name', (1, 4), 'v', ('Store',)), ('Name', (1, 9), 'v', ('Load',)), [('Pass', (1, 11))], [], None)], []),
 ('Module', [('While', (1, 0), ('Name', (1, 6), 'v', ('Load',)), [('Pass', (1, 8))], [])], []),
 ('Module', [('If', (1, 0), ('Name', (1, 3), 'v', ('Load',)), [('Pass', (1, 5))], [])], []),
 ('Module', [('With', (1, 0), [('withitem', ('Name', (1, 5), 'x', ('Load',)), ('Name', (1, 10), 'y', ('Store',)))], [('Pass', (1, 13))], None)], []),
 ('Module', [('With', (1, 0), [('withitem', ('Name', (1, 5), 'x', ('Load',)), ('Name', (1, 10), 'y', ('Store',))), ('withitem', ('Name', (1, 13), 'z', ('Load',)), ('Name', (1, 18), 'q', ('Store',)))], [('Pass', (1, 21))], None)], []),
-('Module', [('Raise', (1, 0), ('Call', (1, 6), ('Name', (1, 6), 'Exception', ('Load',)), [('Constant', (1, 16), 'string')], []), None)], []),
+('Module', [('Raise', (1, 0), ('Call', (1, 6), ('Name', (1, 6), 'Exception', ('Load',)), [('Constant', (1, 16), 'string', None)], []), None)], []),
 ('Module', [('Try', (1, 0), [('Pass', (2, 2))], [('ExceptHandler', (3, 0), ('Name', (3, 7), 'Exception', ('Load',)), None, [('Pass', (4, 2))])], [], [])], []),
 ('Module', [('Try', (1, 0), [('Pass', (2, 2))], [], [], [('Pass', (4, 2))])], []),
 ('Module', [('Assert', (1, 0), ('Name', (1, 7), 'v', ('Load',)), None)], []),
 ('Module', [('Import', (1, 0), [('alias', 'sys', None)])], []),
 ('Module', [('ImportFrom', (1, 0), 'sys', [('alias', 'v', None)], 0)], []),
 ('Module', [('Global', (1, 0), ['v'])], []),
-('Module', [('Expr', (1, 0), ('Constant', (1, 0), 1))], []),
+('Module', [('Expr', (1, 0), ('Constant', (1, 0), 1, None))], []),
 ('Module', [('Pass', (1, 0))], []),
 ('Module', [('For', (1, 0), ('Name', (1, 4), 'v', ('Store',)), ('Name', (1, 9), 'v', ('Load',)), [('Break', (1, 11))], [], None)], []),
 ('Module', [('For', (1, 0), ('Name', (1, 4), 'v', ('Store',)), ('Name', (1, 9), 'v', ('Load',)), [('Continue', (1, 11))], [], None)], []),
@@ -1649,11 +1667,11 @@ exec_results = [
 ('Module', [('Expr', (1, 0), ('DictComp', (1, 0), ('Name', (1, 1), 'a', ('Load',)), ('Name', (1, 5), 'b', ('Load',)), [('comprehension', ('Tuple', (1, 11), [('Name', (1, 11), 'v', ('Store',)), ('Name', (1, 13), 'w', ('Store',))], ('Store',)), ('Name', (1, 18), 'x', ('Load',)), [], 0)]))], []),
 ('Module', [('Expr', (1, 0), ('SetComp', (1, 0), ('Name', (1, 1), 'r', ('Load',)), [('comprehension', ('Name', (1, 7), 'l', ('Store',)), ('Name', (1, 12), 'x', ('Load',)), [('Name', (1, 17), 'g', ('Load',))], 0)]))], []),
 ('Module', [('Expr', (1, 0), ('SetComp', (1, 0), ('Name', (1, 1), 'r', ('Load',)), [('comprehension', ('Tuple', (1, 7), [('Name', (1, 7), 'l', ('Store',)), ('Name', (1, 9), 'm', ('Store',))], ('Store',)), ('Name', (1, 14), 'x', ('Load',)), [], 0)]))], []),
-('Module', [('AsyncFunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('Expr', (2, 1), ('Constant', (2, 1), 'async function')), ('Expr', (3, 1), ('Await', (3, 1), ('Call', (3, 7), ('Name', (3, 7), 'something', ('Load',)), [], [])))], [], None, None)], []),
-('Module', [('AsyncFunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('AsyncFor', (2, 1), ('Name', (2, 11), 'e', ('Store',)), ('Name', (2, 16), 'i', ('Load',)), [('Expr', (2, 19), ('Constant', (2, 19), 1))], [('Expr', (3, 7), ('Constant', (3, 7), 2))], None)], [], None, None)], []),
-('Module', [('AsyncFunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('AsyncWith', (2, 1), [('withitem', ('Name', (2, 12), 'a', ('Load',)), ('Name', (2, 17), 'b', ('Store',)))], [('Expr', (2, 20), ('Constant', (2, 20), 1))], None)], [], None, None)], []),
-('Module', [('Expr', (1, 0), ('Dict', (1, 0), [None, ('Constant', (1, 10), 2)], [('Dict', (1, 3), [('Constant', (1, 4), 1)], [('Constant', (1, 6), 2)]), ('Constant', (1, 12), 3)]))], []),
-('Module', [('Expr', (1, 0), ('Set', (1, 0), [('Starred', (1, 1), ('Set', (1, 2), [('Constant', (1, 3), 1), ('Constant', (1, 6), 2)]), ('Load',)), ('Constant', (1, 10), 3)]))], []),
+('Module', [('AsyncFunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('Expr', (2, 1), ('Constant', (2, 1), 'async function', None)), ('Expr', (3, 1), ('Await', (3, 1), ('Call', (3, 7), ('Name', (3, 7), 'something', ('Load',)), [], [])))], [], None, None)], []),
+('Module', [('AsyncFunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('AsyncFor', (2, 1), ('Name', (2, 11), 'e', ('Store',)), ('Name', (2, 16), 'i', ('Load',)), [('Expr', (2, 19), ('Constant', (2, 19), 1, None))], [('Expr', (3, 7), ('Constant', (3, 7), 2, None))], None)], [], None, None)], []),
+('Module', [('AsyncFunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('AsyncWith', (2, 1), [('withitem', ('Name', (2, 12), 'a', ('Load',)), ('Name', (2, 17), 'b', ('Store',)))], [('Expr', (2, 20), ('Constant', (2, 20), 1, None))], None)], [], None, None)], []),
+('Module', [('Expr', (1, 0), ('Dict', (1, 0), [None, ('Constant', (1, 10), 2, None)], [('Dict', (1, 3), [('Constant', (1, 4), 1, None)], [('Constant', (1, 6), 2, None)]), ('Constant', (1, 12), 3, None)]))], []),
+('Module', [('Expr', (1, 0), ('Set', (1, 0), [('Starred', (1, 1), ('Set', (1, 2), [('Constant', (1, 3), 1, None), ('Constant', (1, 6), 2, None)]), ('Load',)), ('Constant', (1, 10), 3, None)]))], []),
 ('Module', [('AsyncFunctionDef', (1, 0), 'f', ('arguments', [], None, [], [], None, []), [('Expr', (2, 1), ('ListComp', (2, 1), ('Name', (2, 2), 'i', ('Load',)), [('comprehension', ('Name', (2, 14), 'b', ('Store',)), ('Name', (2, 19), 'c', ('Load',)), [], 1)]))], [], None, None)], []),
 ('Module', [('FunctionDef', (3, 0), 'f', ('arguments', [], None, [], [], None, []), [('Pass', (3, 9))], [('Name', (1, 1), 'deco1', ('Load',)), ('Call', (2, 0), ('Name', (2, 1), 'deco2', ('Load',)), [], [])], None, None)], []),
 ('Module', [('AsyncFunctionDef', (3, 0), 'f', ('arguments', [], None, [], [], None, []), [('Pass', (3, 15))], [('Name', (1, 1), 'deco1', ('Load',)), ('Call', (2, 0), ('Name', (2, 1), 'deco2', ('Load',)), [], [])], None, None)], []),
@@ -1661,18 +1679,18 @@ exec_results = [
 ('Module', [('FunctionDef', (2, 0), 'f', ('arguments', [], None, [], [], None, []), [('Pass', (2, 9))], [('Call', (1, 1), ('Name', (1, 1), 'deco', ('Load',)), [('GeneratorExp', (1, 5), ('Name', (1, 6), 'a', ('Load',)), [('comprehension', ('Name', (1, 12), 'a', ('Store',)), ('Name', (1, 17), 'b', ('Load',)), [], 0)])], [])], None, None)], []),
 ]
 single_results = [
-('Interactive', [('Expr', (1, 0), ('BinOp', (1, 0), ('Constant', (1, 0), 1), ('Add',), ('Constant', (1, 2), 2)))]),
+('Interactive', [('Expr', (1, 0), ('BinOp', (1, 0), ('Constant', (1, 0), 1, None), ('Add',), ('Constant', (1, 2), 2, None)))]),
 ]
 eval_results = [
-('Expression', ('Constant', (1, 0), None)),
+('Expression', ('Constant', (1, 0), None, None)),
 ('Expression', ('BoolOp', (1, 0), ('And',), [('Name', (1, 0), 'a', ('Load',)), ('Name', (1, 6), 'b', ('Load',))])),
 ('Expression', ('BinOp', (1, 0), ('Name', (1, 0), 'a', ('Load',)), ('Add',), ('Name', (1, 4), 'b', ('Load',)))),
 ('Expression', ('UnaryOp', (1, 0), ('Not',), ('Name', (1, 4), 'v', ('Load',)))),
-('Expression', ('Lambda', (1, 0), ('arguments', [], None, [], [], None, []), ('Constant', (1, 7), None))),
-('Expression', ('Dict', (1, 0), [('Constant', (1, 2), 1)], [('Constant', (1, 4), 2)])),
+('Expression', ('Lambda', (1, 0), ('arguments', [], None, [], [], None, []), ('Constant', (1, 7), None, None))),
+('Expression', ('Dict', (1, 0), [('Constant', (1, 2), 1, None)], [('Constant', (1, 4), 2, None)])),
 ('Expression', ('Dict', (1, 0), [], [])),
-('Expression', ('Set', (1, 0), [('Constant', (1, 1), None)])),
-('Expression', ('Dict', (1, 0), [('Constant', (2, 6), 1)], [('Constant', (4, 10), 2)])),
+('Expression', ('Set', (1, 0), [('Constant', (1, 1), None, None)])),
+('Expression', ('Dict', (1, 0), [('Constant', (2, 6), 1, None)], [('Constant', (4, 10), 2, None)])),
 ('Expression', ('ListComp', (1, 0), ('Name', (1, 1), 'a', ('Load',)), [('comprehension', ('Name', (1, 7), 'b', ('Store',)), ('Name', (1, 12), 'c', ('Load',)), [('Name', (1, 17), 'd', ('Load',))], 0)])),
 ('Expression', ('GeneratorExp', (1, 0), ('Name', (1, 1), 'a', ('Load',)), [('comprehension', ('Name', (1, 7), 'b', ('Store',)), ('Name', (1, 12), 'c', ('Load',)), [('Name', (1, 17), 'd', ('Load',))], 0)])),
 ('Expression', ('ListComp', (1, 0), ('Tuple', (1, 1), [('Name', (1, 2), 'a', ('Load',)), ('Name', (1, 4), 'b', ('Load',))], ('Load',)), [('comprehension', ('Tuple', (1, 11), [('Name', (1, 11), 'a', ('Store',)), ('Name', (1, 13), 'b', ('Store',))], ('Store',)), ('Name', (1, 18), 'c', ('Load',)), [], 0)])),
@@ -1684,19 +1702,19 @@ eval_results = [
 ('Expression', ('GeneratorExp', (1, 0), ('Tuple', (1, 1), [('Name', (1, 2), 'a', ('Load',)), ('Name', (1, 4), 'b', ('Load',))], ('Load',)), [('comprehension', ('Tuple', (1, 11), [('Name', (1, 11), 'a', ('Store',)), ('Name', (1, 13), 'b', ('Store',))], ('Store',)), ('Name', (1, 18), 'c', ('Load',)), [], 0)])),
 ('Expression', ('GeneratorExp', (1, 0), ('Tuple', (1, 1), [('Name', (1, 2), 'a', ('Load',)), ('Name', (1, 4), 'b', ('Load',))], ('Load',)), [('comprehension', ('Tuple', (1, 11), [('Name', (1, 12), 'a', ('Store',)), ('Name', (1, 14), 'b', ('Store',))], ('Store',)), ('Name', (1, 20), 'c', ('Load',)), [], 0)])),
 ('Expression', ('GeneratorExp', (1, 0), ('Tuple', (1, 1), [('Name', (1, 2), 'a', ('Load',)), ('Name', (1, 4), 'b', ('Load',))], ('Load',)), [('comprehension', ('List', (1, 11), [('Name', (1, 12), 'a', ('Store',)), ('Name', (1, 14), 'b', ('Store',))], ('Store',)), ('Name', (1, 20), 'c', ('Load',)), [], 0)])),
-('Expression', ('Compare', (1, 0), ('Constant', (1, 0), 1), [('Lt',), ('Lt',)], [('Constant', (1, 4), 2), ('Constant', (1, 8), 3)])),
-('Expression', ('Call', (1, 0), ('Name', (1, 0), 'f', ('Load',)), [('Constant', (1, 2), 1), ('Constant', (1, 4), 2), ('Starred', (1, 10), ('Name', (1, 11), 'd', ('Load',)), ('Load',))], [('keyword', 'c', ('Constant', (1, 8), 3)), ('keyword', None, ('Name', (1, 15), 'e', ('Load',)))])),
+('Expression', ('Compare', (1, 0), ('Constant', (1, 0), 1, None), [('Lt',), ('Lt',)], [('Constant', (1, 4), 2, None), ('Constant', (1, 8), 3, None)])),
+('Expression', ('Call', (1, 0), ('Name', (1, 0), 'f', ('Load',)), [('Constant', (1, 2), 1, None), ('Constant', (1, 4), 2, None), ('Starred', (1, 10), ('Name', (1, 11), 'd', ('Load',)), ('Load',))], [('keyword', 'c', ('Constant', (1, 8), 3, None)), ('keyword', None, ('Name', (1, 15), 'e', ('Load',)))])),
 ('Expression', ('Call', (1, 0), ('Name', (1, 0), 'f', ('Load',)), [('GeneratorExp', (1, 1), ('Name', (1, 2), 'a', ('Load',)), [('comprehension', ('Name', (1, 8), 'a', ('Store',)), ('Name', (1, 13), 'b', ('Load',)), [], 0)])], [])),
-('Expression', ('Constant', (1, 0), 10)),
-('Expression', ('Constant', (1, 0), 'string')),
+('Expression', ('Constant', (1, 0), 10, None)),
+('Expression', ('Constant', (1, 0), 'string', None)),
 ('Expression', ('Attribute', (1, 0), ('Name', (1, 0), 'a', ('Load',)), 'b', ('Load',))),
 ('Expression', ('Subscript', (1, 0), ('Name', (1, 0), 'a', ('Load',)), ('Slice', ('Name', (1, 2), 'b', ('Load',)), ('Name', (1, 4), 'c', ('Load',)), None), ('Load',))),
 ('Expression', ('Name', (1, 0), 'v', ('Load',))),
-('Expression', ('List', (1, 0), [('Constant', (1, 1), 1), ('Constant', (1, 3), 2), ('Constant', (1, 5), 3)], ('Load',))),
+('Expression', ('List', (1, 0), [('Constant', (1, 1), 1, None), ('Constant', (1, 3), 2, None), ('Constant', (1, 5), 3, None)], ('Load',))),
 ('Expression', ('List', (1, 0), [], ('Load',))),
-('Expression', ('Tuple', (1, 0), [('Constant', (1, 0), 1), ('Constant', (1, 2), 2), ('Constant', (1, 4), 3)], ('Load',))),
-('Expression', ('Tuple', (1, 0), [('Constant', (1, 1), 1), ('Constant', (1, 3), 2), ('Constant', (1, 5), 3)], ('Load',))),
+('Expression', ('Tuple', (1, 0), [('Constant', (1, 0), 1, None), ('Constant', (1, 2), 2, None), ('Constant', (1, 4), 3, None)], ('Load',))),
+('Expression', ('Tuple', (1, 0), [('Constant', (1, 1), 1, None), ('Constant', (1, 3), 2, None), ('Constant', (1, 5), 3, None)], ('Load',))),
 ('Expression', ('Tuple', (1, 0), [], ('Load',))),
-('Expression', ('Call', (1, 0), ('Attribute', (1, 0), ('Attribute', (1, 0), ('Attribute', (1, 0), ('Name', (1, 0), 'a', ('Load',)), 'b', ('Load',)), 'c', ('Load',)), 'd', ('Load',)), [('Subscript', (1, 8), ('Attribute', (1, 8), ('Name', (1, 8), 'a', ('Load',)), 'b', ('Load',)), ('Slice', ('Constant', (1, 12), 1), ('Constant', (1, 14), 2), None), ('Load',))], [])),
+('Expression', ('Call', (1, 0), ('Attribute', (1, 0), ('Attribute', (1, 0), ('Attribute', (1, 0), ('Name', (1, 0), 'a', ('Load',)), 'b', ('Load',)), 'c', ('Load',)), 'd', ('Load',)), [('Subscript', (1, 8), ('Attribute', (1, 8), ('Name', (1, 8), 'a', ('Load',)), 'b', ('Load',)), ('Slice', ('Constant', (1, 12), 1, None), ('Constant', (1, 14), 2, None), None), ('Load',))], [])),
 ]
 main()
diff --git a/Misc/NEWS.d/next/Library/2019-03-12-21-02-55.bpo-36280.mOd3iH.rst b/Misc/NEWS.d/next/Library/2019-03-12-21-02-55.bpo-36280.mOd3iH.rst
new file mode 100644
index 0000000000..e97285431e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-03-12-21-02-55.bpo-36280.mOd3iH.rst
@@ -0,0 +1,2 @@
+Add a kind field to ast.Constant. It is 'u' if the literal has a 'u' prefix
+(i.e. a Python 2 style unicode literal), else None.
diff --git a/Parser/Python.asdl b/Parser/Python.asdl
index 1ccd2ca223..c32b65a52f 100644
--- a/Parser/Python.asdl
+++ b/Parser/Python.asdl
@@ -78,7 +78,7 @@ module Python
          | Call(expr func, expr* args, keyword* keywords)
          | FormattedValue(expr value, int? conversion, expr? format_spec)
          | JoinedStr(expr* values)
-         | Constant(constant value)
+         | Constant(constant value, string? kind)
 
          -- the following expression can appear in assignment context
          | Attribute(expr value, identifier attr, expr_context ctx)
diff --git a/Python/Python-ast.c b/Python/Python-ast.c
index 0411f9f07f..d0416eb639 100644
--- a/Python/Python-ast.c
+++ b/Python/Python-ast.c
@@ -324,8 +324,10 @@ static char *JoinedStr_fields[]={
     "values",
 };
 static PyTypeObject *Constant_type;
+_Py_IDENTIFIER(kind);
 static char *Constant_fields[]={
     "value",
+    "kind",
 };
 static PyTypeObject *Attribute_type;
 _Py_IDENTIFIER(attr);
@@ -950,7 +952,7 @@ static int init_types(void)
     if (!FormattedValue_type) return 0;
     JoinedStr_type = make_type("JoinedStr", expr_type, JoinedStr_fields, 1);
     if (!JoinedStr_type) return 0;
-    Constant_type = make_type("Constant", expr_type, Constant_fields, 1);
+    Constant_type = make_type("Constant", expr_type, Constant_fields, 2);
     if (!Constant_type) return 0;
     Attribute_type = make_type("Attribute", expr_type, Attribute_fields, 3);
     if (!Attribute_type) return 0;
@@ -2287,8 +2289,8 @@ JoinedStr(asdl_seq * values, int lineno, int col_offset, int end_lineno, int
 }
 
 expr_ty
-Constant(constant value, int lineno, int col_offset, int end_lineno, int
-         end_col_offset, PyArena *arena)
+Constant(constant value, string kind, int lineno, int col_offset, int
+         end_lineno, int end_col_offset, PyArena *arena)
 {
     expr_ty p;
     if (!value) {
@@ -2301,6 +2303,7 @@ Constant(constant value, int lineno, int col_offset, int end_lineno, int
         return NULL;
     p->kind = Constant_kind;
     p->v.Constant.value = value;
+    p->v.Constant.kind = kind;
     p->lineno = lineno;
     p->col_offset = col_offset;
     p->end_lineno = end_lineno;
@@ -3507,6 +3510,11 @@ ast2obj_expr(void* _o)
         if (_PyObject_SetAttrId(result, &PyId_value, value) == -1)
             goto failed;
         Py_DECREF(value);
+        value = ast2obj_string(o->v.Constant.kind);
+        if (!value) goto failed;
+        if (_PyObject_SetAttrId(result, &PyId_kind, value) == -1)
+            goto failed;
+        Py_DECREF(value);
         break;
     case Attribute_kind:
         result = PyType_GenericNew(Attribute_type, NULL, NULL);
@@ -7224,6 +7232,7 @@ obj2ast_expr(PyObject* obj, expr_ty* out, PyArena* arena)
     }
     if (isinstance) {
         constant value;
+        string kind;
 
         if (_PyObject_LookupAttrId(obj, &PyId_value, &tmp) < 0) {
             return 1;
@@ -7238,8 +7247,21 @@ obj2ast_expr(PyObject* obj, expr_ty* out, PyArena* arena)
             if (res != 0) goto failed;
             Py_CLEAR(tmp);
         }
-        *out = Constant(value, lineno, col_offset, end_lineno, end_col_offset,
-                        arena);
+        if (_PyObject_LookupAttrId(obj, &PyId_kind, &tmp) < 0) {
+            return 1;
+        }
+        if (tmp == NULL || tmp == Py_None) {
+            Py_CLEAR(tmp);
+            kind = NULL;
+        }
+        else {
+            int res;
+            res = obj2ast_string(tmp, &kind, arena);
+            if (res != 0) goto failed;
+            Py_CLEAR(tmp);
+        }
+        *out = Constant(value, kind, lineno, col_offset, end_lineno,
+                        end_col_offset, arena);
         if (*out == NULL) goto failed;
         return 0;
     }
diff --git a/Python/ast.c b/Python/ast.c
index d4ee1b351f..971b8ddc8c 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -2313,13 +2313,13 @@ ast_for_atom(struct compiling *c, const node *n)
         size_t len = strlen(s);
         if (len >= 4 && len <= 5) {
             if (!strcmp(s, "None"))
-                return Constant(Py_None, LINENO(n), n->n_col_offset,
+                return Constant(Py_None, NULL, LINENO(n), n->n_col_offset,
                                 n->n_end_lineno, n->n_end_col_offset, c->c_arena);
             if (!strcmp(s, "True"))
-                return Constant(Py_True, LINENO(n), n->n_col_offset,
+                return Constant(Py_True, NULL, LINENO(n), n->n_col_offset,
                                 n->n_end_lineno, n->n_end_col_offset, c->c_arena);
             if (!strcmp(s, "False"))
-                return Constant(Py_False, LINENO(n), n->n_col_offset,
+                return Constant(Py_False, NULL, LINENO(n), n->n_col_offset,
                                 n->n_end_lineno, n->n_end_col_offset, c->c_arena);
         }
         name = new_identifier(s, c);
@@ -2374,11 +2374,11 @@ ast_for_atom(struct compiling *c, const node *n)
             Py_DECREF(pynum);
             return NULL;
         }
-        return Constant(pynum, LINENO(n), n->n_col_offset,
+        return Constant(pynum, NULL, LINENO(n), n->n_col_offset,
                         n->n_end_lineno, n->n_end_col_offset, c->c_arena);
     }
     case ELLIPSIS: /* Ellipsis */
-        return Constant(Py_Ellipsis, LINENO(n), n->n_col_offset,
+        return Constant(Py_Ellipsis, NULL, LINENO(n), n->n_col_offset,
                         n->n_end_lineno, n->n_end_col_offset, c->c_arena);
     case LPAR: /* some parenthesized expressions */
         ch = CHILD(n, 1);
@@ -5388,18 +5388,57 @@ FstringParser_Dealloc(FstringParser *state)
     ExprList_Dealloc(&state->expr_list);
 }
 
+/* Constants for the following */
+static PyObject *u_kind;
+
+/* Compute 'kind' field for string Constant (either 'u' or None) */
+static PyObject *
+make_kind(struct compiling *c, const node *n)
+{
+    char *s = NULL;
+    PyObject *kind = NULL;
+
+    /* Find the first string literal, if any */
+    while (TYPE(n) != STRING) {
+        if (NCH(n) == 0)
+            return NULL;
+        n = CHILD(n, 0);
+    }
+    REQ(n, STRING);
+
+    /* If it starts with 'u', return a PyUnicode "u" string */
+    s = STR(n);
+    if (s && *s == 'u') {
+        if (!u_kind) {
+            u_kind = PyUnicode_InternFromString("u");
+            if (!u_kind)
+                return NULL;
+        }
+        kind = u_kind;
+        if (PyArena_AddPyObject(c->c_arena, kind) < 0) {
+            return NULL;
+        }
+        Py_INCREF(kind);
+    }
+    return kind;
+}
+
 /* Make a Constant node, but decref the PyUnicode object being added. */
 static expr_ty
 make_str_node_and_del(PyObject **str, struct compiling *c, const node* n)
 {
     PyObject *s = *str;
+    PyObject *kind = NULL;
     *str = NULL;
     assert(PyUnicode_CheckExact(s));
     if (PyArena_AddPyObject(c->c_arena, s) < 0) {
         Py_DECREF(s);
         return NULL;
     }
-    return Constant(s, LINENO(n), n->n_col_offset,
+    kind = make_kind(c, n);
+    if (kind == NULL && PyErr_Occurred())
+        return NULL;
+    return Constant(s, kind, LINENO(n), n->n_col_offset,
                     n->n_end_lineno, n->n_end_col_offset, c->c_arena);
 }
 
@@ -5774,7 +5813,7 @@ parsestrplus(struct compiling *c, const node *n)
         /* Just return the bytes object and we're done. */
         if (PyArena_AddPyObject(c->c_arena, bytes_str) < 0)
             goto error;
-        return Constant(bytes_str, LINENO(n), n->n_col_offset,
+        return Constant(bytes_str, NULL, LINENO(n), n->n_col_offset,
                         n->n_end_lineno, n->n_end_col_offset, c->c_arena);
     }