bpo-37330: open() no longer accept 'U' in file mode (GH-28118)

open(), io.open(), codecs.open() and fileinput.FileInput no longer
accept "U" ("universal newline") in the file mode. This flag was
deprecated since Python 3.3.

Author: vstinner

Doc/library/codecs.rst

@@ -204,6 +204,9 @@ wider range of codecs when working with binary files:
    *buffering* has the same meaning as for the built-in :func:`open` function.
    It defaults to -1 which means that the default buffer size will be used.
 
+   .. versionchanged:: 3.11
+      The ``'U'`` mode has been removed.
+
 
 .. function:: EncodedFile(file, data_encoding, file_encoding=None, errors='strict')
 

Doc/library/fileinput.rst

@@ -153,7 +153,7 @@ available for subclassing as well:
    and :meth:`~io.TextIOBase.readline` cannot be mixed.
 
    With *mode* you can specify which file mode will be passed to :func:`open`. It
-   must be one of ``'r'``, ``'rU'``, ``'U'`` and ``'rb'``.
+   must be one of ``'r'`` and ``'rb'``.
 
    The *openhook*, when given, must be a function that takes two arguments,
    *filename* and *mode*, and returns an accordingly opened file-like object. You
@@ -171,9 +171,6 @@ available for subclassing as well:
    .. versionchanged:: 3.2
       Can be used as a context manager.
 
-   .. deprecated:: 3.4
-      The ``'rU'`` and ``'U'`` modes.
-
    .. deprecated:: 3.8
       Support for :meth:`__getitem__` method is deprecated.
 
@@ -183,6 +180,9 @@ available for subclassing as well:
    .. versionchanged:: 3.10
       The keyword-only parameter *encoding* and *errors* are added.
 
+   .. versionchanged:: 3.11
+      The ``'rU'`` and ``'U'`` modes have been removed.
+
 
 **Optional in-place filtering:** if the keyword argument ``inplace=True`` is
 passed to :func:`fileinput.input` or to the :class:`FileInput` constructor, the

Doc/library/functions.rst

@@ -1156,12 +1156,6 @@ are always available.  They are listed here in alphabetical order.
    first decoded using a platform-dependent encoding or using the specified
    *encoding* if given.
 
-   There is an additional mode character permitted, ``'U'``, which no longer
-   has any effect, and is considered deprecated. It previously enabled
-   :term:`universal newlines` in text mode, which became the default behavior
-   in Python 3.0. Refer to the documentation of the
-   :ref:`newline <open-newline-parameter>` parameter for further details.
-
    .. note::
 
       Python doesn't depend on the underlying operating system's notion of text
@@ -1304,39 +1298,34 @@ are always available.  They are listed here in alphabetical order.
    The ``mode`` and ``flags`` arguments may have been modified or inferred from
    the original call.
 
-   .. versionchanged::
-      3.3
+   .. versionchanged:: 3.3
 
          * The *opener* parameter was added.
          * The ``'x'`` mode was added.
          * :exc:`IOError` used to be raised, it is now an alias of :exc:`OSError`.
          * :exc:`FileExistsError` is now raised if the file opened in exclusive
            creation mode (``'x'``) already exists.
 
-   .. versionchanged::
-      3.4
+   .. versionchanged:: 3.4
 
          * The file is now non-inheritable.
 
-   .. deprecated-removed:: 3.4 3.10
-
-      The ``'U'`` mode.
-
-   .. versionchanged::
-      3.5
+   .. versionchanged:: 3.5
 
          * If the system call is interrupted and the signal handler does not raise an
            exception, the function now retries the system call instead of raising an
            :exc:`InterruptedError` exception (see :pep:`475` for the rationale).
          * The ``'namereplace'`` error handler was added.
 
-   .. versionchanged::
-      3.6
+   .. versionchanged:: 3.6
 
          * Support added to accept objects implementing :class:`os.PathLike`.
          * On Windows, opening a console buffer may return a subclass of
            :class:`io.RawIOBase` other than :class:`io.FileIO`.
 
+   .. versionchanged:: 3.11
+      The ``'U'`` mode has been removed.
+
 .. function:: ord(c)
 
    Given a string representing one Unicode character, return an integer

Doc/whatsnew/3.11.rst

@@ -321,6 +321,14 @@ Changes in the Python API
   Python 3.8.
   (Contributed by Illia Volochii in :issue:`43234`.)
 
+* :func:`open`, :func:`io.open`, :func:`codecs.open` and
+  :class:`fileinput.FileInput` no longer accept ``'U'`` ("universal newline")
+  in the file mode. This flag was deprecated since Python 3.3. In Python 3, the
+  "universal newline" is used by default when a file is open in text mode.  The
+  :ref:`newline parameter <open-newline-parameter>` of :func:`open` controls
+  how universal newlines works.
+  (Contributed by Victor Stinner in :issue:`37330`.)
+
 
 C API Changes
 =============

Lib/_pyio.py

@@ -101,7 +101,6 @@ def open(file, mode="r", buffering=-1, encoding=None, errors=None,
     'b'       binary mode
     't'       text mode (default)
     '+'       open a disk file for updating (reading and writing)
-    'U'       universal newline mode (deprecated)
     ========= ===============================================================
 
     The default mode is 'rt' (open for reading text). For binary random
@@ -117,10 +116,6 @@ def open(file, mode="r", buffering=-1, encoding=None, errors=None,
     returned as strings, the bytes having been first decoded using a
     platform-dependent encoding or using the specified encoding if given.
 
-    'U' mode is deprecated and will raise an exception in future versions
-    of Python.  It has no effect in Python 3.  Use newline to control
-    universal newlines mode.
-
     buffering is an optional integer used to set the buffering policy.
     Pass 0 to switch buffering off (only allowed in binary mode), 1 to select
     line buffering (only usable in text mode), and an integer > 1 to indicate
@@ -206,7 +201,7 @@ def open(file, mode="r", buffering=-1, encoding=None, errors=None,
     if errors is not None and not isinstance(errors, str):
         raise TypeError("invalid errors: %r" % errors)
     modes = set(mode)
-    if modes - set("axrwb+tU") or len(mode) > len(modes):
+    if modes - set("axrwb+t") or len(mode) > len(modes):
         raise ValueError("invalid mode: %r" % mode)
     creating = "x" in modes
     reading = "r" in modes
@@ -215,13 +210,6 @@ def open(file, mode="r", buffering=-1, encoding=None, errors=None,
     updating = "+" in modes
     text = "t" in modes
     binary = "b" in modes
-    if "U" in modes:
-        if creating or writing or appending or updating:
-            raise ValueError("mode U cannot be combined with 'x', 'w', 'a', or '+'")
-        import warnings
-        warnings.warn("'U' mode is deprecated",
-                      DeprecationWarning, 2)
-        reading = True
     if text and binary:
         raise ValueError("can't have text and binary mode at once")
     if creating + reading + writing + appending > 1:

Lib/fileinput.py

@@ -217,15 +217,10 @@ def __init__(self, files=None, inplace=False, backup="", *,
                           EncodingWarning, 2)
 
         # restrict mode argument to reading modes
-        if mode not in ('r', 'rU', 'U', 'rb'):
-            raise ValueError("FileInput opening mode must be one of "
-                             "'r', 'rU', 'U' and 'rb'")
-        if 'U' in mode:
-            import warnings
-            warnings.warn("'U' mode is deprecated",
-                          DeprecationWarning, 2)
+        if mode not in ('r', 'rb'):
+            raise ValueError("FileInput opening mode must be 'r' or 'rb'")
         self._mode = mode
-        self._write_mode = mode.replace('r', 'w') if 'U' not in mode else 'w'
+        self._write_mode = mode.replace('r', 'w')
         if openhook:
             if inplace:
                 raise ValueError("FileInput cannot use an opening hook in inplace mode")

Lib/imp.py

@@ -226,7 +226,7 @@ def load_module(name, file, filename, details):
 
     """
     suffix, mode, type_ = details
-    if mode and (not mode.startswith(('r', 'U')) or '+' in mode):
+    if mode and (not mode.startswith('r') or '+' in mode):
         raise ValueError('invalid file open mode {!r}'.format(mode))
     elif file is None and type_ in {PY_SOURCE, PY_COMPILED}:
         msg = 'file object required for import (type code {})'.format(type_)

Lib/test/test_codecs.py

@@ -714,11 +714,23 @@ def test_bug691291(self):
         self.addCleanup(os_helper.unlink, os_helper.TESTFN)
         with open(os_helper.TESTFN, 'wb') as fp:
             fp.write(s)
-        with warnings_helper.check_warnings(('', DeprecationWarning)):
-            reader = codecs.open(os_helper.TESTFN, 'U', encoding=self.encoding)
-        with reader:
+        with codecs.open(os_helper.TESTFN, 'r',
+                         encoding=self.encoding) as reader:
             self.assertEqual(reader.read(), s1)
 
+    def test_invalid_modes(self):
+        for mode in ('U', 'rU', 'r+U'):
+            with self.assertRaises(ValueError) as cm:
+                codecs.open(os_helper.TESTFN, mode, encoding=self.encoding)
+            self.assertIn('invalid mode', str(cm.exception))
+
+        for mode in ('rt', 'wt', 'at', 'r+t'):
+            with self.assertRaises(ValueError) as cm:
+                codecs.open(os_helper.TESTFN, mode, encoding=self.encoding)
+            self.assertIn("can't have text and binary mode at once",
+                          str(cm.exception))
+
+
 class UTF16LETest(ReadTest, unittest.TestCase):
     encoding = "utf-16-le"
     ill_formed_sequence = b"\x80\xdc"

Lib/test/test_fileinput.py

@@ -230,20 +230,11 @@ def test_fileno(self):
         line = list(fi)
         self.assertEqual(fi.fileno(), -1)
 
-    def test_opening_mode(self):
-        try:
-            # invalid mode, should raise ValueError
-            fi = FileInput(mode="w", encoding="utf-8")
-            self.fail("FileInput should reject invalid mode argument")
-        except ValueError:
-            pass
-        # try opening in universal newline mode
-        t1 = self.writeTmp(b"A\nB\r\nC\rD", mode="wb")
-        with warnings_helper.check_warnings(('', DeprecationWarning)):
-            fi = FileInput(files=t1, mode="U", encoding="utf-8")
-        with warnings_helper.check_warnings(('', DeprecationWarning)):
-            lines = list(fi)
-        self.assertEqual(lines, ["A\n", "B\n", "C\n", "D"])
+    def test_invalid_opening_mode(self):
+        for mode in ('w', 'rU', 'U'):
+            with self.subTest(mode=mode):
+                with self.assertRaises(ValueError):
+                    FileInput(mode=mode)
 
     def test_stdin_binary_mode(self):
         with mock.patch('sys.stdin') as m_stdin:
@@ -1015,10 +1006,6 @@ def check(mode, expected_lines):
             self.assertEqual(lines, expected_lines)
 
         check('r', ['A\n', 'B\n', 'C\n', 'D\u20ac'])
-        with self.assertWarns(DeprecationWarning):
-            check('rU', ['A\n', 'B\n', 'C\n', 'D\u20ac'])
-        with self.assertWarns(DeprecationWarning):
-            check('U', ['A\n', 'B\n', 'C\n', 'D\u20ac'])
         with self.assertRaises(ValueError):
             check('rb', ['A\n', 'B\r\n', 'C\r', 'D\u20ac'])
 

Lib/test/test_io.py

@@ -3954,16 +3954,6 @@ def test_attributes(self):
         self.assertEqual(f.mode, "wb")
         f.close()
 
-        with warnings_helper.check_warnings(('', DeprecationWarning)):
-            f = self.open(os_helper.TESTFN, "U", encoding="utf-8")
-        self.assertEqual(f.name,            os_helper.TESTFN)
-        self.assertEqual(f.buffer.name,     os_helper.TESTFN)
-        self.assertEqual(f.buffer.raw.name, os_helper.TESTFN)
-        self.assertEqual(f.mode,            "U")
-        self.assertEqual(f.buffer.mode,     "rb")
-        self.assertEqual(f.buffer.raw.mode, "rb")
-        f.close()
-
         f = self.open(os_helper.TESTFN, "w+", encoding="utf-8")
         self.assertEqual(f.mode,            "w+")
         self.assertEqual(f.buffer.mode,     "rb+") # Does it really matter?
@@ -3977,6 +3967,13 @@ def test_attributes(self):
         f.close()
         g.close()
 
+    def test_removed_u_mode(self):
+        # bpo-37330: The "U" mode has been removed in Python 3.11
+        for mode in ("U", "rU", "r+U"):
+            with self.assertRaises(ValueError) as cm:
+                self.open(os_helper.TESTFN, mode)
+            self.assertIn('invalid mode', str(cm.exception))
+
     def test_open_pipe_with_append(self):
         # bpo-27805: Ignore ESPIPE from lseek() in open().
         r, w = os.pipe()

Misc/NEWS.d/next/Core and Builtins/2021-09-02-01-28-01.bpo-37330.QDjM_l.rst

@@ -0,0 +1,4 @@
+:func:`open`, :func:`io.open`, :func:`codecs.open` and
+:class:`fileinput.FileInput` no longer accept ``'U'`` ("universal newline")
+in the file mode. This flag was deprecated since Python 3.3. Patch by Victor
+Stinner.

Modules/_io/_iomodule.c

@@ -138,7 +138,6 @@ Character Meaning
 'b'       binary mode
 't'       text mode (default)
 '+'       open a disk file for updating (reading and writing)
-'U'       universal newline mode (deprecated)
 ========= ===============================================================
 
 The default mode is 'rt' (open for reading text). For binary random
@@ -154,10 +153,6 @@ bytes objects without any decoding. In text mode (the default, or when
 returned as strings, the bytes having been first decoded using a
 platform-dependent encoding or using the specified encoding if given.
 
-'U' mode is deprecated and will raise an exception in future versions
-of Python.  It has no effect in Python 3.  Use newline to control
-universal newlines mode.
-
 buffering is an optional integer used to set the buffering policy.
 Pass 0 to switch buffering off (only allowed in binary mode), 1 to select
 line buffering (only usable in text mode), and an integer > 1 to indicate
@@ -233,12 +228,12 @@ static PyObject *
 _io_open_impl(PyObject *module, PyObject *file, const char *mode,
               int buffering, const char *encoding, const char *errors,
               const char *newline, int closefd, PyObject *opener)
-/*[clinic end generated code: output=aefafc4ce2b46dc0 input=7295902222e6b311]*/
+/*[clinic end generated code: output=aefafc4ce2b46dc0 input=1543f4511d2356a5]*/
 {
     unsigned i;
 
     int creating = 0, reading = 0, writing = 0, appending = 0, updating = 0;
-    int text = 0, binary = 0, universal = 0;
+    int text = 0, binary = 0;
 
     char rawmode[6], *m;
     int line_buffering, is_number;
@@ -296,10 +291,6 @@ _io_open_impl(PyObject *module, PyObject *file, const char *mode,
         case 'b':
             binary = 1;
             break;
-        case 'U':
-            universal = 1;
-            reading = 1;
-            break;
         default:
             goto invalid_mode;
         }
@@ -322,18 +313,6 @@ _io_open_impl(PyObject *module, PyObject *file, const char *mode,
     *m = '\0';
 
     /* Parameters validation */
-    if (universal) {
-        if (creating || writing || appending || updating) {
-            PyErr_SetString(PyExc_ValueError,
-                            "mode U cannot be combined with 'x', 'w', 'a', or '+'");
-            goto error;
-        }
-        if (PyErr_WarnEx(PyExc_DeprecationWarning,
-                         "'U' mode is deprecated", 1) < 0)
-            goto error;
-        reading = 1;
-    }
-
     if (text && binary) {
         PyErr_SetString(PyExc_ValueError,
                         "can't have text and binary mode at once");

Modules/_io/clinic/_iomodule.c.h

@@ -36,7 +36,6 @@ PyDoc_STRVAR(_io_open__doc__,
 "\'b\'       binary mode\n"
 "\'t\'       text mode (default)\n"
 "\'+\'       open a disk file for updating (reading and writing)\n"
-"\'U\'       universal newline mode (deprecated)\n"
 "========= ===============================================================\n"
 "\n"
 "The default mode is \'rt\' (open for reading text). For binary random\n"
@@ -52,10 +51,6 @@ PyDoc_STRVAR(_io_open__doc__,
 "returned as strings, the bytes having been first decoded using a\n"
 "platform-dependent encoding or using the specified encoding if given.\n"
 "\n"
-"\'U\' mode is deprecated and will raise an exception in future versions\n"
-"of Python.  It has no effect in Python 3.  Use newline to control\n"
-"universal newlines mode.\n"
-"\n"
 "buffering is an optional integer used to set the buffering policy.\n"
 "Pass 0 to switch buffering off (only allowed in binary mode), 1 to select\n"
 "line buffering (only usable in text mode), and an integer > 1 to indicate\n"
@@ -359,4 +354,4 @@ _io_open_code(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObjec
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=06e055d1d80b835d input=a9049054013a1b77]*/
+/*[clinic end generated code: output=6ea315343f6a94ba input=a9049054013a1b77]*/