bpo-33569 Preserve type information with dataclasses.InitVar (GH-8927)
diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index 75113f1..b035cbb 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -201,10 +201,16 @@
class _InitVarMeta(type):
def __getitem__(self, params):
- return self
+ return InitVar(params)
class InitVar(metaclass=_InitVarMeta):
- pass
+ __slots__ = ('type', )
+
+ def __init__(self, type):
+ self.type = type
+
+ def __repr__(self):
+ return f'dataclasses.InitVar[{self.type.__name__}]'
# Instances of Field are only ever created from within this module,
@@ -586,7 +592,8 @@
def _is_initvar(a_type, dataclasses):
# The module we're checking against is the module we're
# currently in (dataclasses.py).
- return a_type is dataclasses.InitVar
+ return (a_type is dataclasses.InitVar
+ or type(a_type) is dataclasses.InitVar)
def _is_type(annotation, cls, a_module, a_type, is_type_predicate):
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index 8672106..53e8443 100755
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -1097,6 +1097,12 @@
c = C(init_param=10)
self.assertEqual(c.x, 20)
+ def test_init_var_preserve_type(self):
+ self.assertEqual(InitVar[int].type, int)
+
+ # Make sure the repr is correct.
+ self.assertEqual(repr(InitVar[int]), 'dataclasses.InitVar[int]')
+
def test_init_var_inheritance(self):
# Note that this deliberately tests that a dataclass need not
# have a __post_init__ function if it has an InitVar field.