diff -r e18ac7370113 Doc/whatsnew/3.6.rst
--- a/Doc/whatsnew/3.6.rst	Sat Jun 18 13:56:16 2016 +0300
+++ b/Doc/whatsnew/3.6.rst	Sat Jun 18 14:42:37 2016 +0300
@@ -555,6 +555,10 @@ Deprecated Python modules, functions and
   been deprecated in previous versions of Python in favour of
   :meth:`importlib.abc.Loader.exec_module`.
 
+* Undocumented support of general :term:`bytes-like objects <bytes-like object>`
+  as path in :func:`compile` and similar functions is now deprecated.
+  (Contributed by Serhiy Storchaka in :issue:`26754`.)
+
 
 Deprecated functions and types of the C API
 -------------------------------------------
diff -r e18ac7370113 Lib/test/test_compile.py
--- a/Lib/test/test_compile.py	Sat Jun 18 13:56:16 2016 +0300
+++ b/Lib/test/test_compile.py	Sat Jun 18 14:42:37 2016 +0300
@@ -473,10 +473,13 @@ if 1:
         self.assertEqual(d, {1: 2, 3: 4})
 
     def test_compile_filename(self):
-        for filename in ('file.py', b'file.py',
-                         bytearray(b'file.py'), memoryview(b'file.py')):
+        for filename in 'file.py', b'file.py':
             code = compile('pass', filename, 'exec')
             self.assertEqual(code.co_filename, 'file.py')
+        for filename in bytearray(b'file.py'), memoryview(b'file.py'):
+            with self.assertWarns(DeprecationWarning):
+                code = compile('pass', filename, 'exec')
+            self.assertEqual(code.co_filename, 'file.py')
         self.assertRaises(TypeError, compile, 'pass', list(b'file.py'), 'exec')
 
     @support.cpython_only
diff -r e18ac7370113 Lib/test/test_parser.py
--- a/Lib/test/test_parser.py	Sat Jun 18 13:56:16 2016 +0300
+++ b/Lib/test/test_parser.py	Sat Jun 18 14:42:37 2016 +0300
@@ -632,12 +632,18 @@ class CompileTestCase(unittest.TestCase)
         self.assertEqual(code.co_filename, '<syntax-tree>')
         code = st.compile()
         self.assertEqual(code.co_filename, '<syntax-tree>')
-        for filename in ('file.py', b'file.py',
-                         bytearray(b'file.py'), memoryview(b'file.py')):
+        for filename in 'file.py', b'file.py':
             code = parser.compilest(st, filename)
             self.assertEqual(code.co_filename, 'file.py')
             code = st.compile(filename)
             self.assertEqual(code.co_filename, 'file.py')
+        for filename in bytearray(b'file.py'), memoryview(b'file.py'):
+            with self.assertWarns(DeprecationWarning):
+                code = parser.compilest(st, filename)
+            self.assertEqual(code.co_filename, 'file.py')
+            with self.assertWarns(DeprecationWarning):
+                code = st.compile(filename)
+            self.assertEqual(code.co_filename, 'file.py')
         self.assertRaises(TypeError, parser.compilest, st, list(b'file.py'))
         self.assertRaises(TypeError, st.compile, list(b'file.py'))
 
diff -r e18ac7370113 Lib/test/test_symtable.py
--- a/Lib/test/test_symtable.py	Sat Jun 18 13:56:16 2016 +0300
+++ b/Lib/test/test_symtable.py	Sat Jun 18 14:42:37 2016 +0300
@@ -158,9 +158,11 @@ class SymtableTest(unittest.TestCase):
         checkfilename("def f(x): foo)(")  # parse-time
         checkfilename("def f(x): global x")  # symtable-build-time
         symtable.symtable("pass", b"spam", "exec")
-        with self.assertRaises(TypeError):
+        with self.assertWarns(DeprecationWarning), \
+             self.assertRaises(TypeError):
             symtable.symtable("pass", bytearray(b"spam"), "exec")
-        symtable.symtable("pass", memoryview(b"spam"), "exec")
+        with self.assertWarns(DeprecationWarning):
+            symtable.symtable("pass", memoryview(b"spam"), "exec")
         with self.assertRaises(TypeError):
             symtable.symtable("pass", list(b"spam"), "exec")
 
diff -r e18ac7370113 Lib/test/test_zipimport.py
--- a/Lib/test/test_zipimport.py	Sat Jun 18 13:56:16 2016 +0300
+++ b/Lib/test/test_zipimport.py	Sat Jun 18 14:42:37 2016 +0300
@@ -629,8 +629,10 @@ class UncompressedZipImportTestCase(Impo
 
         zipimport.zipimporter(filename)
         zipimport.zipimporter(os.fsencode(filename))
-        zipimport.zipimporter(bytearray(os.fsencode(filename)))
-        zipimport.zipimporter(memoryview(os.fsencode(filename)))
+        with self.assertWarns(DeprecationWarning):
+            zipimport.zipimporter(bytearray(os.fsencode(filename)))
+        with self.assertWarns(DeprecationWarning):
+            zipimport.zipimporter(memoryview(os.fsencode(filename)))
 
 
 @support.requires_zlib
diff -r e18ac7370113 Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Sat Jun 18 13:56:16 2016 +0300
+++ b/Objects/unicodeobject.c	Sat Jun 18 14:42:37 2016 +0300
@@ -3837,7 +3837,13 @@ PyUnicode_FSDecoder(PyObject* arg, void*
         output = arg;
         Py_INCREF(output);
     }
-    else if (PyObject_CheckBuffer(arg)) {
+    else if (PyBytes_Check(arg) || PyObject_CheckBuffer(arg)) {
+        if (!PyBytes_Check(arg) &&
+            PyErr_WarnFormat(PyExc_DeprecationWarning, 1,
+            "path should be string or bytes, not %.200s",
+            Py_TYPE(arg)->tp_name)) {
+            return 0;
+        }
         arg = PyBytes_FromObject(arg);
         if (!arg)
             return 0;
@@ -3846,11 +3852,6 @@ PyUnicode_FSDecoder(PyObject* arg, void*
         Py_DECREF(arg);
         if (!output)
             return 0;
-        if (!PyUnicode_Check(output)) {
-            Py_DECREF(output);
-            PyErr_SetString(PyExc_TypeError, "decoder failed to return unicode");
-            return 0;
-        }
     }
     else {
         PyErr_Format(PyExc_TypeError,