Support double-stringified annotations in dataclasses

python · gvanrossum · Oct 6, 2020 · May 27, 2020 · May 27, 2020 · May 27, 2020
commit 0a04da8a9d4bac80e0e912bbf8c62599dc3e65d1
diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
@@ -652,6 +652,12 @@ def _is_type(annotation, cls, a_module, a_type, is_type_predicate):
     # a eval() penalty for every single field of every dataclass
     # that's defined.  It was judged not worth it.
 
+    # Strip away the extra quotes as a result of double-stringifying when the
+    # 'annotations' feature became default.
+    if annotation.startswith(("'", '"')) and annotation.endswith(("'", '"')):
+        annotation = annotation[1:-1]
+
+
     match = _MODULE_IDENTIFIER_RE.match(annotation)
     if match:
         ns = None

diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
@@ -2805,6 +2805,13 @@ class C:
 
 
 class TestStringAnnotations(unittest.TestCase):
+    def test_double_stringification(self):
+        @dataclass
+        class T:
+            a: "typing.ClassVar[int]"
+
+        T()
+
     def test_classvar(self):
         # These tests assume that both "import typing" and "from
         # typing import *" have been run in this file.