* break the asciify-paths code out into the util.asciify_paths function

* make asciifying handle both os.sep and os.altsep (testing needed as I
  don't have a windows box handy)
* make %asciify{} use the same code path as the asciify_paths goop.
* added a discrete test to %asciify{} so my life acts as a warning to
  others
* changelog note now with 80% less antihistamine-induced runon sentences

beets/library.py

@@ -23,7 +23,6 @@ import unicodedata
 import time
 import re
 import six
-from unidecode import unidecode
 
 from beets import logging
 from beets.mediafile import MediaFile, UnreadableFileError
@@ -824,13 +823,10 @@ class Item(LibModel):
             subpath = unicodedata.normalize('NFC', subpath)
 
         if beets.config['asciify_paths']:
-            path_components = subpath.split(os.path.sep)
-            sep_replace = beets.config['path_sep_replace'].get()
-            for index, item in enumerate(path_components):
-                path_components[index] = unidecode(item).replace(
-                    os.path.sep, sep_replace
-                )
-            subpath = os.path.sep.join(path_components)
+            subpath = util.asciify_path(
+                subpath,
+                beets.config['path_sep_replace'].as_str()
+            )
 
         maxlen = beets.config['max_filename_length'].get(int)
         if not maxlen:
@@ -1082,7 +1078,10 @@ class Album(LibModel):
             beets.config['art_filename'].as_str())
         subpath = self.evaluate_template(filename_tmpl, True)
         if beets.config['asciify_paths']:
-            subpath = unidecode(subpath)
+            subpath = util.asciify_path(
+                subpath,
+                beets.config['path_sep_replace'].as_str()
+            )
         subpath = util.sanitize_path(subpath,
                                      replacements=self._db.replacements)
         subpath = bytestring_path(subpath)
@@ -1434,7 +1433,7 @@ class DefaultTemplateFunctions(object):
     def tmpl_asciify(s):
         """Translate non-ASCII characters to their ASCII equivalents.
         """
-        return unidecode(s)
+        return util.asciify_path(s, beets.config['path_sep_replace'].as_str())
 
     @staticmethod
     def tmpl_time(s, fmt):

beets/util/__init__.py

@@ -29,6 +29,7 @@ import platform
 import shlex
 from beets.util import hidden
 import six
+from unidecode import unidecode
 
 
 MAX_FILENAME_LENGTH = 200
@@ -941,3 +942,22 @@ def raw_seconds_short(string):
         raise ValueError(u'String not in M:SS format')
     minutes, seconds = map(int, match.groups())
     return float(minutes * 60 + seconds)
+
+
+def asciify_path(path, sep_replace):
+    """Decodes all unicode characters in a path into ASCII equivalents.
+
+    Substitutions are provided by the unidecode module. Path separators in the
+    input are preserved.
+
+    Keyword arguments:
+    path -- The path to be asciified.
+    sep_replace -- the string to be used to replace extraneous path separators.
+    """
+    # if this platform has an os.altsep, change it to os.sep.
+    if os.altsep:
+        path.replace(os.altsep, os.sep)
+    path_components = path.split(os.sep)
+    for index, item in enumerate(path_components):
+        path_components[index] = unidecode(item).replace(os.sep, sep_replace)
+    return os.sep.join(path_components)

docs/changelog.rst

@@ -7,7 +7,9 @@ Changelog
 Fixes:
 
 * :doc:`/plugins/badfiles`: Fix a crash on non-ASCII filenames. :bug:`2299`
-* With :ref:`asciify-paths` set to "yes", some unicode tags could decode in such a way that erroneous directories were created mid-filename. This has been fixed.
+* The ``%asciify{}`` path formatting function and the :ref:`asciify-paths` 
+  setting properly substitute path separators generated by converting some 
+  unicode characters into ASCII, such as ½ and ¢.
 
 
 1.4.1 (November 25, 2016)

test/test_library.py

@@ -589,6 +589,10 @@ class DestinationFunctionTest(_common.TestCase, PathFormattingMixin):
         self._setf(u'%title{$title}')
         self._assert_dest(b'/base/The Title')
 
+    def test_asciify_variable(self):
+        self._setf(u'%asciify{ab\xa2\xbdd}')
+        self._assert_dest(b'/base/abC_1_2d')
+
     def test_left_variable(self):
         self._setf(u'%left{$title, 3}')
         self._assert_dest(b'/base/the')