bpo-29240: PEP 540: Add a new UTF-8 Mode (#855)

* Add -X utf8 command line option, PYTHONUTF8 environment variable
  and a new sys.flags.utf8_mode flag.
* If the LC_CTYPE locale is "C" at startup: enable automatically the
  UTF-8 mode.
* Add _winapi.GetACP(). encodings._alias_mbcs() now calls
  _winapi.GetACP() to get the ANSI code page
* locale.getpreferredencoding() now returns 'UTF-8' in the UTF-8
  mode. As a side effect, open() now uses the UTF-8 encoding by
  default in this mode.
* Py_DecodeLocale() and Py_EncodeLocale() now use the UTF-8 encoding
  in the UTF-8 Mode.
* Update subprocess._args_from_interpreter_flags() to handle -X utf8
* Skip some tests relying on the current locale if the UTF-8 mode is
  enabled.
* Add test_utf8mode.py.
* _Py_DecodeUTF8_surrogateescape() gets a new optional parameter to
  return also the length (number of wide characters).
* pymain_get_global_config() and pymain_set_global_config() now
  always copy flag values, rather than only copying if the new value
  is greater than the old value.

1 files changed, 6 insertions, 0 deletions

diff --git a/Lib/locale.py b/Lib/locale.py
index f1d157d..18079e7 100644
--- a/Lib/locale.py
+++ b/Lib/locale.py
@@ -617,6 +617,8 @@ if sys.platform.startswith("win"):
     # On Win32, this will return the ANSI code page
     def getpreferredencoding(do_setlocale = True):
         """Return the charset that the user is likely using."""
+        if sys.flags.utf8_mode:
+            return 'UTF-8'
         import _bootlocale
         return _bootlocale.getpreferredencoding(False)
 else:
@@ -634,6 +636,8 @@ else:
             def getpreferredencoding(do_setlocale = True):
                 """Return the charset that the user is likely using,
                 by looking at environment variables."""
+                if sys.flags.utf8_mode:
+                    return 'UTF-8'
                 res = getdefaultlocale()[1]
                 if res is None:
                     # LANG not set, default conservatively to ASCII
@@ -643,6 +647,8 @@ else:
         def getpreferredencoding(do_setlocale = True):
             """Return the charset that the user is likely using,
             according to the system configuration."""
+            if sys.flags.utf8_mode:
+                return 'UTF-8'
             import _bootlocale
             if do_setlocale:
                 oldloc = setlocale(LC_CTYPE)