Fix some Python warnings about unknown/unnecessary string escape sequences.

Cython/Compiler/TreePath.py

@@ -12,14 +12,14 @@ import re
 import operator
 
 path_tokenizer = re.compile(
-    "("
-    "'[^']*'|\"[^\"]*\"|"
-    "//?|"
-    "\(\)|"
-    "==?|"
-    "[/.*\[\]\(\)@])|"
-    "([^/\[\]\(\)@=\s]+)|"
-    "\s+"
+    r"("
+    r"'[^']*'|\"[^\"]*\"|"
+    r"//?|"
+    r"\(\)|"
+    r"==?|"
+    r"[/.*\[\]()@])|"
+    r"([^/\[\]()@=\s]+)|"
+    r"\s+"
     ).findall
 
 def iterchildren(node, attr_name):