[3.8] bpo-32912: Revert SyntaxWarning on invalid escape sequences (GH-15142)

* bpo-32912: Revert warnings for invalid escape sequences.

DeprecationWarning will continue to be emitted for invalid escape sequences in string and bytes literals in 3.8 just as it did in 3.7.

SyntaxWarning may be emitted in the future. But per mailing list discussion, we don't yet know when because we haven't settled on how to do so in a non-disruptive manner.

diff --git a/Doc/reference/lexical_analysis.rst b/Doc/reference/lexical_analysis.rst
index cc1b2f57a70e3b8b544e8d1175fe6933471fbdbc..7e1e17edb2d8da302276a8818762c8baa9d276d1 100644 (file)
--- a/Doc/reference/lexical_analysis.rst
+++ b/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

diff --git a/Doc/whatsnew/3.8.rst b/Doc/whatsnew/3.8.rst
index 9f70582745147b1965f0e9a454be0f1bc5ccb7f8..83caa2cc5abc43f10e9fc88219d2cf4673c1cdab 100644 (file)
--- a/Doc/whatsnew/3.8.rst
+++ b/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::
 

diff --git a/Lib/test/test_fstring.py b/Lib/test/test_fstring.py
index fb761441fcee5cfec18fd33be276759a88b6a1b4..49663923e7f5aa2e52c04a4e01514d4bc0d05459 100644 (file)
--- a/Lib/test/test_fstring.py
+++ b/Lib/test/test_fstring.py
@@ -649,7 +649,7 @@ non-important content
         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')

diff --git a/Lib/test/test_string_literals.py b/Lib/test/test_string_literals.py
index 5961d591c448035149d88d018e29b28279250df0..0cea2edc32afa29eaceff983903830b9a3bc8da8 100644 (file)
--- a/Lib/test/test_string_literals.py
+++ b/Lib/test/test_string_literals.py
@@ -32,6 +32,7 @@ import sys
 import shutil
 import tempfile
 import unittest
+import warnings
 
 
 TEMPLATE = r"""# coding: %s
@@ -110,10 +111,24 @@ class TestLiterals(unittest.TestCase):
         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 @@ class TestLiterals(unittest.TestCase):
         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')

diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-08-06-14-03-59.bpo-32912.UDwSMJ.rst b/Misc/NEWS.d/next/Core and Builtins/2019-08-06-14-03-59.bpo-32912.UDwSMJ.rst
new file mode 100644 (file)
index 0000000..e18d8ad
--- /dev/null
+++ b/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.

diff --git a/Python/ast.c b/Python/ast.c
index f6c2049ae2cfdf20ffcc2e61b47a70480b81d1b3..9947824de7446ce42cf22fa053b7ea604edca236 100644 (file)
--- a/Python/ast.c
+++ b/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);