Initial python3 changes

Mostly just updating libraries, removing string encoding/decoding,
fixing some edge cases. No new functionality was added in this
commit.

lib/beetsplug/bpm.py

@@ -0,0 +1,87 @@
+# This file is part of beets.
+# Copyright 2016, aroquen
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+
+"""Determine BPM by pressing a key to the rhythm."""
+
+
+import time
+
+from beets import ui
+from beets.plugins import BeetsPlugin
+
+
+def bpm(max_strokes):
+    """Returns average BPM (possibly of a playing song)
+    listening to Enter keystrokes.
+    """
+    t0 = None
+    dt = []
+    for i in range(max_strokes):
+        # Press enter to the rhythm...
+        s = input()
+        if s == '':
+            t1 = time.time()
+            # Only start measuring at the second stroke
+            if t0:
+                dt.append(t1 - t0)
+            t0 = t1
+        else:
+            break
+
+    # Return average BPM
+    # bpm = (max_strokes-1) / sum(dt) * 60
+    ave = sum([1.0 / dti * 60 for dti in dt]) / len(dt)
+    return ave
+
+
+class BPMPlugin(BeetsPlugin):
+
+    def __init__(self):
+        super().__init__()
+        self.config.add({
+            'max_strokes': 3,
+            'overwrite': True,
+        })
+
+    def commands(self):
+        cmd = ui.Subcommand('bpm',
+                            help='determine bpm of a song by pressing '
+                            'a key to the rhythm')
+        cmd.func = self.command
+        return [cmd]
+
+    def command(self, lib, opts, args):
+        items = lib.items(ui.decargs(args))
+        write = ui.should_write()
+        self.get_bpm(items, write)
+
+    def get_bpm(self, items, write=False):
+        overwrite = self.config['overwrite'].get(bool)
+        if len(items) > 1:
+            raise ValueError('Can only get bpm of one song at time')
+
+        item = items[0]
+        if item['bpm']:
+            self._log.info('Found bpm {0}', item['bpm'])
+            if not overwrite:
+                return
+
+        self._log.info('Press Enter {0} times to the rhythm or Ctrl-D '
+                       'to exit', self.config['max_strokes'].get(int))
+        new_bpm = bpm(self.config['max_strokes'].get(int))
+        item['bpm'] = int(new_bpm)
+        if write:
+            item.try_write()
+        item.store()
+        self._log.info('Added new bpm {0}', item['bpm'])