[2.7] bpo-8765: Deprecate writing unicode to binary streams in Py3k mode.

Lib/test/test_fileio.py

@@ -12,7 +12,7 @@
 from UserList import UserList
 
 from test.test_support import TESTFN, check_warnings, run_unittest, make_bad_fd
-from test.test_support import py3k_bytes as bytes, cpython_only
+from test.test_support import py3k_bytes as bytes, cpython_only, check_py3k_warnings
 from test.script_helper import run_python
 
 from _io import FileIO as _FileIO
@@ -101,6 +101,10 @@ def test_none_args(self):
         self.assertEqual(self.f.readline(None), b"hi\n")
         self.assertEqual(self.f.readlines(None), [b"bye\n", b"abc"])
 
+    def testWriteUnicode(self):
+        with check_py3k_warnings():
+            self.f.write(u'')
+
     def testRepr(self):
         self.assertEqual(repr(self.f), "<_io.FileIO name=%r mode='%s'>"
                                        % (self.f.name, self.f.mode))
@@ -210,7 +214,7 @@ def testErrnoOnClose(self, f):
 
     @ClosedFDRaises
     def testErrnoOnClosedWrite(self, f):
-        f.write('a')
+        f.write(b'a')
 
     @ClosedFDRaises
     def testErrnoOnClosedSeek(self, f):

Misc/NEWS.d/next/Library/2018-12-12-09-59-41.bpo-8765.IFupT2.rst

@@ -0,0 +1,2 @@
+The write() method of buffered and unbuffered binary streams in the io
+module emits now a DeprecationWarning in Py3k mode for unicode argument.

Modules/_io/bufferedio.c

@@ -1812,6 +1812,13 @@ bufferedwriter_write(buffered *self, PyObject *args)
     if (!PyArg_ParseTuple(args, "s*:write", &buf)) {
         return NULL;
     }
+    if (PyUnicode_Check(PyTuple_GET_ITEM(args, 0)) &&
+        PyErr_WarnPy3k("write() argument must be string or buffer, "
+                       "not 'unicode'", 1) < 0)
+    {
+        PyBuffer_Release(&buf);
+        return NULL;
+    }
 
     if (IS_CLOSED(self)) {
         PyErr_SetString(PyExc_ValueError, "write to closed file");

Modules/_io/fileio.c

@@ -716,8 +716,16 @@ fileio_write(fileio *self, PyObject *args)
     if (!self->writable)
         return err_mode("writing");
 
-    if (!PyArg_ParseTuple(args, "s*", &pbuf))
+    if (!PyArg_ParseTuple(args, "s*:write", &pbuf)) {
         return NULL;
+    }
+    if (PyUnicode_Check(PyTuple_GET_ITEM(args, 0)) &&
+        PyErr_WarnPy3k("write() argument must be string or buffer, "
+                       "not 'unicode'", 1) < 0)
+    {
+        PyBuffer_Release(&pbuf);
+        return NULL;
+    }
 
     if (_PyVerify_fd(self->fd)) {
         Py_BEGIN_ALLOW_THREADS