wip: tcr compression

regex flags do not need "u" when the search string does not make use of the feature

In python3, re.U is the default for unicode strings. For byte strings,
which is what we use, it is a fatal error.

src/calibre/ebooks/compression/tcr.py

@@ -1,5 +1,4 @@
 # -*- coding: utf-8 -*-
-
 from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__ = 'GPL 3'
@@ -35,10 +34,10 @@ def _combine_codes(self):
         The intent is to create more unused codes.
         '''
         possible_codes = []
-        a_code = set(re.findall(b'(?msu).', self.coded_txt))
+        a_code = set(re.findall(b'(?ms).', self.coded_txt))
 
         for code in a_code:
-            single_code = set(re.findall(b'(?msu)%s.' % re.escape(code), self.coded_txt))
+            single_code = set(re.findall(b'(?ms)%s.' % re.escape(code), self.coded_txt))
             if len(single_code) == 1:
                 possible_codes.append(single_code.pop())
 
@@ -60,7 +59,7 @@ def _new_codes(self):
         '''
         Create new codes from codes that occur in pairs often.
         '''
-        possible_new_codes = list(set(re.findall(b'(?msu)..', self.coded_txt)))
+        possible_new_codes = list(set(re.findall(b'(?ms)..', self.coded_txt)))
         new_codes_count = []
 
         for c in possible_new_codes:
@@ -77,7 +76,7 @@ def _new_codes(self):
     def compress(self, txt):
         self._reset()
 
-        self.codes = list(set(re.findall(b'(?msu).', txt)))
+        self.codes = list(set(re.findall(b'(?ms).', txt)))
 
         # Replace the text with their corresponding code
         for c in txt: