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/unimported.py

@@ -0,0 +1,68 @@
+# This file is part of beets.
+# Copyright 2019, Joris Jensen
+#
+# 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.
+
+"""
+List all files in the library folder which are not listed in the
+ beets library database, including art files
+"""
+
+import os
+
+from beets import util
+from beets.plugins import BeetsPlugin
+from beets.ui import Subcommand, print_
+
+__author__ = 'https://github.com/MrNuggelz'
+
+
+class Unimported(BeetsPlugin):
+
+    def __init__(self):
+        super().__init__()
+        self.config.add(
+            {
+                'ignore_extensions': []
+            }
+        )
+
+    def commands(self):
+        def print_unimported(lib, opts, args):
+            ignore_exts = [
+                ('.' + x).encode()
+                for x in self.config["ignore_extensions"].as_str_seq()
+            ]
+            ignore_dirs = [
+                os.path.join(lib.directory, x.encode())
+                for x in self.config["ignore_subdirectories"].as_str_seq()
+            ]
+            in_folder = {
+                os.path.join(r, file)
+                for r, d, f in os.walk(lib.directory)
+                for file in f
+                if not any(
+                    [file.endswith(ext) for ext in ignore_exts]
+                    + [r in ignore_dirs]
+                )
+            }
+            in_library = {x.path for x in lib.items()}
+            art_files = {x.artpath for x in lib.albums()}
+            for f in in_folder - in_library - art_files:
+                print_(util.displayable_path(f))
+
+        unimported = Subcommand(
+            'unimported',
+            help='list all files in the library folder which are not listed'
+                 ' in the beets library database')
+        unimported.func = print_unimported
+        return [unimported]