Remove raw Unicode literals (fix #2069)

PEP 414 didn't add `ur"..."` literals to Python 3. So for hybrid 2/3
compatibility, these had to be replaced with ordinary Unicode string literals.
This was only painful for one string; the others were only raw strings by
convention. (All were regexes.)

beets/autotag/mb.py

@@ -376,7 +376,7 @@ def _parse_id(s):
     no ID can be found, return None.
     """
     # Find the first thing that looks like a UUID/MBID.
-    match = re.search(ur'[a-f0-9]{8}(-[a-f0-9]{4}){3}-[a-f0-9]{12}', s)
+    match = re.search(u'[a-f0-9]{8}(-[a-f0-9]{4}){3}-[a-f0-9]{12}', s)
     if match:
         return match.group()
 

beetsplug/replaygain.py

@@ -222,9 +222,9 @@ class Bs1770gainBackend(Backend):
         out = []
         data = text.decode('utf8', errors='ignore')
         regex = re.compile(
-            ur'(\s{2,2}\[\d+\/\d+\].*?|\[ALBUM\].*?)'
-            '(?=\s{2,2}\[\d+\/\d+\]|\s{2,2}\[ALBUM\]'
-            ':|done\.\s)', re.DOTALL | re.UNICODE)
+            u'(\\s{2,2}\\[\\d+\\/\\d+\\].*?|\\[ALBUM\\].*?)'
+            '(?=\\s{2,2}\\[\\d+\\/\\d+\\]|\\s{2,2}\\[ALBUM\\]'
+            ':|done\\.\\s)', re.DOTALL | re.UNICODE)
         results = re.findall(regex, data)
         for parts in results[0:num_lines]:
             part = parts.split(b'\n')

test/test_ui.py

@@ -760,7 +760,7 @@ class ConfigTest(unittest.TestCase, TestHelper, _common.Assertions):
 
         ui._raw_main(['test'])
         replacements = self.test_cmd.lib.replacements
-        self.assertEqual(replacements, [(re.compile(ur'[xy]'), 'z')])
+        self.assertEqual(replacements, [(re.compile(u'[xy]'), 'z')])
 
     def test_multiple_replacements_parsed(self):
         with self.write_config_file() as config:
@@ -769,8 +769,8 @@ class ConfigTest(unittest.TestCase, TestHelper, _common.Assertions):
         ui._raw_main(['test'])
         replacements = self.test_cmd.lib.replacements
         self.assertEqual(replacements, [
-            (re.compile(ur'[xy]'), u'z'),
-            (re.compile(ur'foo'), u'bar'),
+            (re.compile(u'[xy]'), u'z'),
+            (re.compile(u'foo'), u'bar'),
         ])
 
     def test_cli_config_option(self):