[3.8] bpo-32912: Revert warnings for invalid escape sequences.

Doc/reference/lexical_analysis.rst

@@ -594,11 +594,9 @@ escape sequences only recognized in string literals fall into the category of
 unrecognized escapes for bytes literals.
 
  .. versionchanged:: 3.6
- Unrecognized escape sequences produce a :exc:`DeprecationWarning`.
-
- .. versionchanged:: 3.8
- Unrecognized escape sequences produce a :exc:`SyntaxWarning`. In
- some future version of Python they will be a :exc:`SyntaxError`.
+ Unrecognized escape sequences produce a :exc:`DeprecationWarning`. In
+ a future Python version they will be a :exc:`SyntaxWarning` and
+ eventually a :exc:`SyntaxError`.
 
 Even in a raw literal, quotes can be escaped with a backslash, but the
 backslash remains in the result; for example, ``r"\""`` is a valid string

Doc/whatsnew/3.8.rst

@@ -414,11 +414,6 @@ Other Language Changes
  and :keyword:`return` statements.
  (Contributed by David Cuthbert and Jordan Chapman in :issue:`32117`.)
 
-* A backslash-character pair that is not a valid escape sequence generates
- a :exc:`DeprecationWarning` since Python 3.6. In Python 3.8 it generates
- a :exc:`SyntaxWarning` instead.
- (Contributed by Serhiy Storchaka in :issue:`32912`.)
-
 * The compiler now produces a :exc:`SyntaxWarning` in some cases when a comma
  is missed before tuple or list. For example::
 

Lib/test/test_fstring.py

@@ -649,7 +649,7 @@ def test_backslashes_in_string_part(self):
  self.assertEqual(f'2\x203', '2 3')
  self.assertEqual(f'\x203', ' 3')
 
- with self.assertWarns(SyntaxWarning): # invalid escape sequence
+ with self.assertWarns(DeprecationWarning): # invalid escape sequence
  value = eval(r"f'\{6*7}'")
  self.assertEqual(value, '\\42')
  self.assertEqual(f'\\{6*7}', '\\42')

Lib/test/test_string_literals.py

@@ -32,6 +32,7 @@
 import shutil
 import tempfile
 import unittest
+import warnings
 
 
 TEMPLATE = r"""# coding: %s
@@ -110,10 +111,24 @@ def test_eval_str_invalid_escape(self):
  for b in range(1, 128):
  if b in b"""\n\r"'01234567NU\\abfnrtuvx""":
  continue
- with self.assertWarns(SyntaxWarning):
+ with self.assertWarns(DeprecationWarning):
  self.assertEqual(eval(r"'\%c'" % b), '\\' + chr(b))
 
- self.check_syntax_warning("'''\n\\z'''")
+ with warnings.catch_warnings(record=True) as w:
+ warnings.simplefilter('always', category=DeprecationWarning)
+ eval("'''\n\\z'''")
+ self.assertEqual(len(w), 1)
+ self.assertEqual(w[0].filename, '<string>')
+ self.assertEqual(w[0].lineno, 1)
+
+ with warnings.catch_warnings(record=True) as w:
+ warnings.simplefilter('error', category=DeprecationWarning)
+ with self.assertRaises(SyntaxError) as cm:
+ eval("'''\n\\z'''")
+ exc = cm.exception
+ self.assertEqual(w, [])
+ self.assertEqual(exc.filename, '<string>')
+ self.assertEqual(exc.lineno, 1)
 
  def test_eval_str_raw(self):
  self.assertEqual(eval(""" r'x' """), 'x')
@@ -145,10 +160,24 @@ def test_eval_bytes_invalid_escape(self):
  for b in range(1, 128):
  if b in b"""\n\r"'01234567\\abfnrtvx""":
  continue
- with self.assertWarns(SyntaxWarning):
+ with self.assertWarns(DeprecationWarning):
  self.assertEqual(eval(r"b'\%c'" % b), b'\\' + bytes([b]))
 
- self.check_syntax_warning("b'''\n\\z'''")
+ with warnings.catch_warnings(record=True) as w:
+ warnings.simplefilter('always', category=DeprecationWarning)
+ eval("b'''\n\\z'''")
+ self.assertEqual(len(w), 1)
+ self.assertEqual(w[0].filename, '<string>')
+ self.assertEqual(w[0].lineno, 1)
+
+ with warnings.catch_warnings(record=True) as w:
+ warnings.simplefilter('error', category=DeprecationWarning)
+ with self.assertRaises(SyntaxError) as cm:
+ eval("b'''\n\\z'''")
+ exc = cm.exception
+ self.assertEqual(w, [])
+ self.assertEqual(exc.filename, '<string>')
+ self.assertEqual(exc.lineno, 1)
 
  def test_eval_bytes_raw(self):
  self.assertEqual(eval(""" br'x' """), b'x')

Misc/NEWS.d/next/Core and Builtins/2019-08-06-14-03-59.bpo-32912.UDwSMJ.rst

@@ -0,0 +1,3 @@
+Reverted :issue:`32912`: emitting :exc:`SyntaxWarning` instead of
+:exc:`DeprecationWarning` for invalid escape sequences in string and bytes
+literals.

Python/ast.c

@@ -4674,12 +4674,12 @@ warn_invalid_escape_sequence(struct compiling *c, const node *n,
  if (msg == NULL) {
  return -1;
  }
- if (PyErr_WarnExplicitObject(PyExc_SyntaxWarning, msg,
+ if (PyErr_WarnExplicitObject(PyExc_DeprecationWarning, msg,
  c->c_filename, LINENO(n),
  NULL, NULL) < 0)
  {
- if (PyErr_ExceptionMatches(PyExc_SyntaxWarning)) {
- /* Replace the SyntaxWarning exception with a SyntaxError
+ if (PyErr_ExceptionMatches(PyExc_DeprecationWarning)) {
+ /* Replace the DeprecationWarning exception with a SyntaxError
  to get a more accurate error report */
  PyErr_Clear();
  ast_error(c, n, "%U", msg);