Require Unicode format strings

Fallout from #2188. Following @jrobeson's suggestion, I just turned the check
in LibModel.__format__ into an assert. This turned up a few badly-behaved
clients, which are also fixed.

beets/library.py

@@ -338,12 +338,8 @@ class LibModel(dbcore.Model):
     def __format__(self, spec):
         if not spec:
             spec = beets.config[self._format_config_key].as_str()
-        result = self.evaluate_template(spec)
-        if isinstance(spec, bytes):
-            # if spec is a byte string then we must return a one as well
-            return result.encode('utf-8')
-        else:
-            return result
+        assert isinstance(spec, six.text_type)
+        return self.evaluate_template(spec)
 
     def __str__(self):
         return format(self)

beetsplug/info.py

@@ -20,7 +20,6 @@ from __future__ import division, absolute_import, print_function
 
 import os
 import re
-import six
 
 from beets.plugins import BeetsPlugin
 from beets import ui
@@ -92,7 +91,7 @@ def print_data(data, item=None, fmt=None):
     """
     if fmt:
         # use fmt specified by the user
-        ui.print_(six.text_type(format(item, fmt)))
+        ui.print_(format(item, fmt))
         return
 
     path = displayable_path(item.path) if item else None
@@ -205,7 +204,8 @@ class InfoPlugin(BeetsPlugin):
                 if opts.keys_only:
                     print_data_keys(data, item)
                 else:
-                    print_data(data, item, opts.format)
+                    fmt = ui.decargs([opts.format])[0]
+                    print_data(data, item, fmt)
                 first = False
 
         if opts.summarize:

beetsplug/mbsubmit.py

@@ -36,7 +36,7 @@ class MBSubmitPlugin(BeetsPlugin):
         super(MBSubmitPlugin, self).__init__()
 
         self.config.add({
-            'format': '$track. $title - $artist ($length)',
+            'format': u'$track. $title - $artist ($length)',
             'threshold': 'medium',
         })
 
@@ -57,4 +57,4 @@ class MBSubmitPlugin(BeetsPlugin):
 
     def print_tracks(self, session, task):
         for i in task.items:
-            print_data(None, i, self.config['format'].get())
+            print_data(None, i, self.config['format'].as_str())

test/test_library.py

@@ -1055,12 +1055,12 @@ class TemplateTest(_common.LibTestCase):
         self.assertEqual(six.text_type(album), u"foö bar")
         self.assertEqual(bytes(album), b"fo\xc3\xb6 bar")
 
-        config['format_item'] = 'bar $foo'
+        config['format_item'] = u'bar $foo'
         item = beets.library.Item()
         item.foo = u'bar'
         item.tagada = u'togodo'
-        self.assertEqual("{0}".format(item), u"bar bar")
-        self.assertEqual("{0:$tagada}".format(item), u"togodo")
+        self.assertEqual(u"{0}".format(item), u"bar bar")
+        self.assertEqual(u"{0:$tagada}".format(item), u"togodo")
 
 
 class UnicodePathTest(_common.LibTestCase):