bpo-43510: Implement PEP 597 opt-in EncodingWarning. (GH-19481)
See [PEP 597](https://www.python.org/dev/peps/pep-0597/).
* Add `-X warn_default_encoding` and `PYTHONWARNDEFAULTENCODING`.
* Add EncodingWarning
* Add io.text_encoding()
* open(), TextIOWrapper() emits EncodingWarning when encoding is omitted and warn_default_encoding is enabled.
* _pyio.TextIOWrapper() uses UTF-8 as fallback default encoding used when failed to import locale module. (used during building Python)
* bz2, configparser, gzip, lzma, pathlib, tempfile modules use io.text_encoding().
* What's new entry
diff --git a/Lib/test/test_pickle.py b/Lib/test/test_pickle.py
index 1f5cb10..23c7bd2 100644
--- a/Lib/test/test_pickle.py
+++ b/Lib/test/test_pickle.py
@@ -483,7 +483,8 @@ def test_exceptions(self):
if exc in (BlockingIOError,
ResourceWarning,
StopAsyncIteration,
- RecursionError):
+ RecursionError,
+ EncodingWarning):
continue
if exc is not OSError and issubclass(exc, OSError):
self.assertEqual(reverse_mapping('builtins', name),