#27364: Deprecate invalid escape strings in str/byutes.

Patch by Emanuel Barry, reviewed by Serhiy Storchaka and Martin Panter.

2 files changed, 9 insertions, 0 deletions

diff --git a/Doc/reference/lexical_analysis.rst b/Doc/reference/lexical_analysis.rst
index b3b71af..48f2043 100644
--- a/Doc/reference/lexical_analysis.rst
+++ b/Doc/reference/lexical_analysis.rst
@@ -560,6 +560,10 @@ is more easily recognized as broken.)  It is also important to note that the
 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 DeprecationWarning.  In
+      some future version of Python they will be a 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
 literal consisting of two characters: a backslash and a double quote; ``r"\"``
diff --git a/Doc/whatsnew/3.6.rst b/Doc/whatsnew/3.6.rst
index e53d48e..a76ac9d 100644
--- a/Doc/whatsnew/3.6.rst
+++ b/Doc/whatsnew/3.6.rst
@@ -952,6 +952,11 @@ Deprecated features
   parameter will be dropped in a future Python release and likely earlier
   through third party tools. See :issue:`27919` for details.
 
+* A backslash-character pair that is not a valid escape sequence now generates
+  a DeprecationWarning.  Although this will eventually become a SyntaxError,
+  that will not be for several Python releases.  (Contributed by Emanuel Barry
+  in :issue:`27364`.)
+
 
 Deprecated Python behavior
 --------------------------