bpo-38605: Make 'from __future__ import annotations' the default (GH-20434)
The hard part was making all the tests pass; there are some subtle issues here, because apparently the future import wasn't tested very thoroughly in previous Python versions.
For example, `inspect.signature()` returned type objects normally (except for forward references), but strings with the future import. We changed it to try and return type objects by calling `typing.get_type_hints()`, but fall back on returning strings if that function fails (which it may do if there are future references in the annotations that require passing in a specific namespace to resolve).
diff --git a/Lib/test/test_opcodes.py b/Lib/test/test_opcodes.py
index 527aca6..1152eb6 100644
--- a/Lib/test/test_opcodes.py
+++ b/Lib/test/test_opcodes.py
@@ -39,7 +39,7 @@
def test_use_existing_annotations(self):
ns = {'__annotations__': {1: 2}}
exec('x: int', ns)
- self.assertEqual(ns['__annotations__'], {'x': int, 1: 2})
+ self.assertEqual(ns['__annotations__'], {'x': 'int', 1: 2})
def test_do_not_recreate_annotations(self):
# Don't rely on the existence of the '__annotations__' global.