bpo-47000: Make io.text_encoding() respects UTF-8 mode

Doc/library/io.rst

@@ -198,12 +198,13 @@ High-level Module Interface
  This is a helper function for callables that use :func:`open` or
  :class:`TextIOWrapper` and have an ``encoding=None`` parameter.
 
- This function returns *encoding* if it is not ``None`` and ``"locale"`` if
- *encoding* is ``None``.
+ This function returns *encoding* if it is not ``None``.
+ Otherwise, it returns ``"locale"`` or ``"utf-8"`` depending on
+ :ref:`UTF-8 Mode <utf8-mode>`.
 
  This function emits an :class:`EncodingWarning` if
  :data:`sys.flags.warn_default_encoding <sys.flags>` is true and *encoding*
- is None. *stacklevel* specifies where the warning is emitted.
+ is ``None``. *stacklevel* specifies where the warning is emitted.
  For example::
 
  def read_text(path, encoding=None):
@@ -218,6 +219,10 @@ High-level Module Interface
 
  .. versionadded:: 3.10
 
+ .. versionchanged:: 3.11
+ :func:`text_encoding` returns "utf-8" when UTF-8 mode is enabled and
+ *encoding* is ``None``.
+
 
 .. exception:: BlockingIOError
 

Include/internal/pycore_global_strings.h

@@ -48,6 +48,7 @@ struct _Py_global_strings {
  STRUCT_FOR_STR(newline, "\n")
  STRUCT_FOR_STR(open_br, "{")
  STRUCT_FOR_STR(percent, "%")
+ STRUCT_FOR_STR(utf_8, "utf-8")
  } literals;
 
  struct {

Include/internal/pycore_runtime_init.h

@@ -672,6 +672,7 @@ extern "C" {
  INIT_STR(newline, "\n"), \
  INIT_STR(open_br, "{"), \
  INIT_STR(percent, "%"), \
+ INIT_STR(utf_8, "utf-8"), \
  }, \
  .identifiers = { \
  INIT_ID(False), \

Lib/_pyio.py

@@ -44,8 +44,9 @@ def text_encoding(encoding, stacklevel=2):
  """
  A helper function to choose the text encoding.
 
- When encoding is not None, just return it.
- Otherwise, return the default text encoding (i.e. "locale").
+ When encoding is not None, this function returns it.
+ Otherwise, this function returns the default text encoding
+ (i.e. "locale" or "utf-8" depends on UTF-8 mode).
 
  This function emits an EncodingWarning if *encoding* is None and
  sys.flags.warn_default_encoding is true.
@@ -55,7 +56,10 @@ def text_encoding(encoding, stacklevel=2):
  However, please consider using encoding="utf-8" for new APIs.
  """
  if encoding is None:
- encoding = "locale"
+ if sys.flags.utf8_mode:
+ encoding = "utf-8"
+ else:
+ encoding = "locale"
  if sys.flags.warn_default_encoding:
  import warnings
  warnings.warn("'encoding' argument not specified.",

Lib/test/test_io.py

@@ -4289,6 +4289,17 @@ def test_check_encoding_warning(self):
  self.assertTrue(
  warnings[1].startswith(b"<string>:8: EncodingWarning: "))
 
+ def test_text_encoding(self):
+ # PEP 597, bpo-47000. io.text_encoding() returns "locale" or "utf-8"
+ # based on sys.flags.utf8_mode
+ code = "import io; print(io.text_encoding(None))"
+
+ proc = assert_python_ok('-X', 'utf8=0', '-c', code)
+ self.assertEqual(b"locale", proc.out.strip())
+
+ proc = assert_python_ok('-X', 'utf8=1', '-c', code)
+ self.assertEqual(b"utf-8", proc.out.strip())
+
  @support.cpython_only
  # Depending if OpenWrapper was already created or not, the warning is
  # emitted or not. For example, the attribute is already created when this

Lib/test/test_utf8_mode.py

@@ -161,7 +161,7 @@ def test_io(self):
  filename = __file__
 
  out = self.get_output('-c', code, filename, PYTHONUTF8='1')
- self.assertEqual(out, 'UTF-8/strict')
+ self.assertEqual(out.lower(), 'utf-8/strict')
 
  def _check_io_encoding(self, module, encoding=None, errors=None):
  filename = __file__
@@ -183,10 +183,10 @@ def _check_io_encoding(self, module, encoding=None, errors=None):
  PYTHONUTF8='1')
 
  if not encoding:
- encoding = 'UTF-8'
+ encoding = 'utf-8'
  if not errors:
  errors = 'strict'
- self.assertEqual(out, f'{encoding}/{errors}')
+ self.assertEqual(out.lower(), f'{encoding}/{errors}')
 
  def check_io_encoding(self, module):
  self._check_io_encoding(module, encoding="latin1")

Misc/NEWS.d/next/Library/2022-03-20-13-00-08.bpo-47000.p8HpG0.rst

@@ -0,0 +1 @@
+Make :func:`io.text_encoding` returns "utf-8" when UTF-8 mode is enabled.

Modules/_io/_iomodule.c

@@ -457,8 +457,9 @@ _io.text_encoding
 
 A helper function to choose the text encoding.
 
-When encoding is not None, just return it.
-Otherwise, return the default text encoding (i.e. "locale").
+When encoding is not None, this function returns it.
+Otherwise, this function returns the default text encoding
+(i.e. "locale" or "utf-8" depends on UTF-8 mode).
 
 This function emits an EncodingWarning if encoding is None and
 sys.flags.warn_default_encoding is true.
@@ -469,7 +470,7 @@ However, please consider using encoding="utf-8" for new APIs.
 
 static PyObject *
 _io_text_encoding_impl(PyObject *module, PyObject *encoding, int stacklevel)
-/*[clinic end generated code: output=91b2cfea6934cc0c input=bf70231213e2a7b4]*/
+/*[clinic end generated code: output=91b2cfea6934cc0c input=4999aa8b3d90f3d4]*/
 {
  if (encoding == NULL || encoding == Py_None) {
  PyInterpreterState *interp = _PyInterpreterState_GET();
@@ -479,7 +480,14 @@ _io_text_encoding_impl(PyObject *module, PyObject *encoding, int stacklevel)
  return NULL;
  }
  }
- return &_Py_ID(locale);
+ const PyPreConfig *preconfig = &_PyRuntime.preconfig;
+ if (preconfig->utf8_mode) {
+ _Py_DECLARE_STR(utf_8, "utf-8");
+ encoding = &_Py_STR(utf_8);
+ }
+ else {
+ encoding = &_Py_ID(locale);
+ }
  }
  Py_INCREF(encoding);
  return encoding;

Python/sysmodule.c

@@ -841,7 +841,10 @@ static PyObject *
 sys_getdefaultencoding_impl(PyObject *module)
 /*[clinic end generated code: output=256d19dfcc0711e6 input=d416856ddbef6909]*/
 {
- return PyUnicode_FromString(PyUnicode_GetDefaultEncoding());
+ _Py_DECLARE_STR(utf_8, "utf-8");
+ PyObject *ret = &_Py_STR(utf_8);
+ Py_INCREF(ret);
+ return ret;
 }
 
 /*[clinic input]