#27364: fix "incorrect" uses of escape character in the stdlib.

And most of the tools.

Patch by Emanual Barry, reviewed by me, Serhiy Storchaka, and
Martin Panter.

Lib/xml/etree/ElementPath.py

@@ -59,15 +59,15 @@
 import re
 
 xpath_tokenizer_re = re.compile(
-    "("
-    "'[^']*'|\"[^\"]*\"|"
-    "::|"
-    "//?|"
-    "\.\.|"
-    "\(\)|"
-    "[/.*:\[\]\(\)@=])|"
-    "((?:\{[^}]+\})?[^/\[\]\(\)@=\s]+)|"
-    "\s+"
+    r"("
+    r"'[^']*'|\"[^\"]*\"|"
+    r"::|"
+    r"//?|"
+    r"\.\.|"
+    r"\(\)|"
+    r"[/.*:\[\]\(\)@=])|"
+    r"((?:\{[^}]+\})?[^/\[\]\(\)@=\s]+)|"
+    r"\s+"
     )
 
 def xpath_tokenizer(pattern, namespaces=None):
@@ -180,7 +180,7 @@ def prepare_predicate(next, token):
                 if elem.get(key) == value:
                     yield elem
         return select
-    if signature == "-" and not re.match("\-?\d+$", predicate[0]):
+    if signature == "-" and not re.match(r"\-?\d+$", predicate[0]):
         # [tag]
         tag = predicate[0]
         def select(context, result):
@@ -188,7 +188,7 @@ def prepare_predicate(next, token):
                 if elem.find(tag) is not None:
                     yield elem
         return select
-    if signature == "-='" and not re.match("\-?\d+$", predicate[0]):
+    if signature == "-='" and not re.match(r"\-?\d+$", predicate[0]):
         # [tag='value']
         tag = predicate[0]
         value = predicate[-1]

Lib/xml/etree/ElementTree.py

@@ -1030,7 +1030,7 @@ def register_namespace(prefix, uri):
     ValueError is raised if prefix is reserved or is invalid.
 
     """
-    if re.match("ns\d+$", prefix):
+    if re.match(r"ns\d+$", prefix):
         raise ValueError("Prefix format reserved for internal use")
     for k, v in list(_namespace_map.items()):
         if k == uri or v == prefix: