Apply most best practices of PEP 8

This refactoring includes:
- Two empty lines before each global function
- Using '{0} {1}'.format(str1, str2) instead of str1 + ' ' + str2
  Sometimes this will make lines longer, sometimes shorter.
- Starting all comments with # + space + comment
- Make lines not longer than 80 characters in most cases
- Renaming some variables to make more sense
- Add some missing code like returns and Exceptions

Not included, but follows:
- Make some comments docstrings
- Rename all 'file' variables, only for Python 2
- Remove some way too verbose comments ;)

core/metadata.py

@@ -9,8 +9,10 @@ try:
 except ImportError:
     import urllib.request as urllib2
 
+
 # check if input file title matches with expected title
 def compare(file, metadata):
+    already_tagged = False
     try:
         if file.endswith('.mp3'):
             audiofile = EasyID3('Music/' + file)
@@ -22,9 +24,10 @@ def compare(file, metadata):
             # fetch track title metadata
             already_tagged = audiofile[tags['title']] == metadata['name']
     except KeyError:
-            already_tagged = False
+        pass
     return already_tagged
 
+
 def embed(music_file, meta_tags):
     if sys.version_info < (3, 0):
         music_file = music_file.encode('utf-8')
@@ -41,6 +44,7 @@ def embed(music_file, meta_tags):
         print('Cannot embed meta-tags into given output extension')
         return False
 
+
 def embed_mp3(music_file, meta_tags):
     # EasyID3 is fun to use ;)
     audiofile = EasyID3('Music/' + music_file)
@@ -48,7 +52,8 @@ def embed_mp3(music_file, meta_tags):
     audiofile['albumartist'] = meta_tags['artists'][0]['name']
     audiofile['album'] = meta_tags['album']['name']
     audiofile['title'] = meta_tags['name']
-    audiofile['tracknumber'] = [meta_tags['track_number'], meta_tags['total_tracks']]
+    audiofile['tracknumber'] = [meta_tags['track_number'],
+                                meta_tags['total_tracks']]
     audiofile['discnumber'] = [meta_tags['disc_number'], 0]
     audiofile['date'] = meta_tags['release_date']
     audiofile['originaldate'] = meta_tags['release_date']
@@ -68,11 +73,13 @@ def embed_mp3(music_file, meta_tags):
     audiofile.save(v2_version=3)
     audiofile = ID3('Music/' + music_file)
     albumart = urllib2.urlopen(meta_tags['album']['images'][0]['url'])
-    audiofile["APIC"] = APIC(encoding=3, mime='image/jpeg', type=3, desc=u'Cover', data=albumart.read())
+    audiofile["APIC"] = APIC(encoding=3, mime='image/jpeg', type=3,
+                             desc=u'Cover', data=albumart.read())
     albumart.close()
     audiofile.save(v2_version=3)
     return True
 
+
 def embed_m4a(music_file, meta_tags):
     # Apple has specific tags - see mutagen docs -
     # http://mutagen.readthedocs.io/en/latest/api/mp4.html
@@ -98,7 +105,8 @@ def embed_m4a(music_file, meta_tags):
     audiofile[tags['albumartist']] = meta_tags['artists'][0]['name']
     audiofile[tags['album']] = meta_tags['album']['name']
     audiofile[tags['title']] = meta_tags['name']
-    audiofile[tags['tracknumber']] = [(meta_tags['track_number'], meta_tags['total_tracks'])]
+    audiofile[tags['tracknumber']] = [(meta_tags['track_number'],
+                                       meta_tags['total_tracks'])]
     audiofile[tags['disknumber']] = [(meta_tags['disc_number'], 0)]
     audiofile[tags['date']] = meta_tags['release_date']
     audiofile[tags['originaldate']] = meta_tags['release_date']
@@ -107,7 +115,8 @@ def embed_m4a(music_file, meta_tags):
     if meta_tags['copyright']:
         audiofile[tags['copyright']] = meta_tags['copyright']
     albumart = urllib2.urlopen(meta_tags['album']['images'][0]['url'])
-    audiofile[tags['albumart']] = [ MP4Cover(albumart.read(), imageformat=MP4Cover.FORMAT_JPEG) ]
+    audiofile[tags['albumart']] = [MP4Cover(
+        albumart.read(), imageformat=MP4Cover.FORMAT_JPEG)]
     albumart.close()
     audiofile.save()
     return True