Avoid re-compiling regular expression

While the re module caches some of the latest compilations, it's better
form to not rely on it doing so.

Signed-off-by: Rodrigo Tobar <rtobar@icrar.org>

Author: rtobar

babel/messages/pofile.py

@@ -26,6 +26,8 @@
     from typing_extensions import Literal
 
 
+_ESCAPED_CHARACTER_PATTERN = re.compile(r'\\([\\trn"])')
+
 def unescape(string: str) -> str:
     r"""Reverse `escape` the given string.
 
@@ -46,7 +48,7 @@ def replace_escapes(match):
             return '\r'
         # m is \ or "
         return m
-    return re.compile(r'\\([\\trn"])').sub(replace_escapes, string[1:-1])
+    return _ESCAPED_CHARACTER_PATTERN.sub(replace_escapes, string[1:-1])
 
 
 def denormalize(string: str) -> str: