From b8213181f22185f09206ad09dc231e4902b5be53 Mon Sep 17 00:00:00 2001
From: "nathdwek@laptop" <nathdwek@ulb.ac.be>
Date: Wed, 16 Nov 2016 23:08:00 +0100
Subject: [PATCH] drop IdentityFallbackDict:

Used by mediafile to determine the preferred extension of an image
That solution looked cool for 2 days, but in hindsight it was pretty bad
---
 beets/mediafile.py        |  6 +++---
 beets/util/collections.py | 30 ------------------------------
 2 files changed, 3 insertions(+), 33 deletions(-)
 delete mode 100644 beets/util/collections.py

diff --git a/beets/mediafile.py b/beets/mediafile.py
index 784695c1a..87a9d10a6 100644
--- a/beets/mediafile.py
+++ b/beets/mediafile.py
@@ -59,7 +59,6 @@ import enum
 
 from beets import logging
 from beets.util import displayable_path, syspath, as_string
-from beets.util.collections import IdentityFallbackDict
 import six
 
 
@@ -82,7 +81,7 @@ TYPES = {
     'aiff': 'AIFF',
 }
 
-PREFERRED_IMAGE_EXTENSIONS = IdentityFallbackDict({'jpeg': 'jpg'})
+PREFERRED_IMAGE_EXTENSIONS = {'jpeg': 'jpg'}
 
 
 # Exceptions.
@@ -355,7 +354,8 @@ def image_mime_type(data):
 
 
 def image_extension(data):
-    return PREFERRED_IMAGE_EXTENSIONS[_imghdr_what_wrapper(data)]
+    ext = _imghdr_what_wrapper(data)
+    return PREFERRED_IMAGE_EXTENSIONS.get(ext, ext)
 
 
 class ImageType(enum.Enum):
diff --git a/beets/util/collections.py b/beets/util/collections.py
deleted file mode 100644
index 696dc9a98..000000000
--- a/beets/util/collections.py
+++ /dev/null
@@ -1,30 +0,0 @@
-# -*- coding: utf-8 -*-
-# This file is part of beets.
-# Copyright 2016, Adrian Sampson.
-#
-# 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.
-
-"""Custom collections classes.
-"""
-
-from __future__ import division, absolute_import, print_function
-
-
-class IdentityFallbackDict(dict):
-    """A dictionary which is "transparent" (maps keys to themselves) for all
-    keys not in it.
-    """
-    def __getitem__(self, key):
-        try:
-            return dict.__getitem__(self, key)
-        except KeyError:
-            return key