Improve a bit the typing, again

libmat2/abstract.py

 import abc
 import os
+from typing import Set
 
 
 class AbstractParser(abc.ABC):
-    meta_list = set()
-    mimetypes = set()
+    meta_list = set()  # type: Set[str]
+    mimetypes = set()  # type: Set[str]
 
-    def __init__(self, filename: str):
+    def __init__(self, filename: str) -> None:
         self.filename = filename
         fname, extension = os.path.splitext(filename)
         self.output_filename = fname + '.cleaned' + extension

libmat2/harmless.py

@@ -5,7 +5,7 @@ class HarmlessParser(abstract.AbstractParser):
     """ This is the parser for filetypes that do not contain metadata. """
     mimetypes = {'application/xml', 'text/plain'}
 
-    def __init__(self, filename: str):
+    def __init__(self, filename: str) -> None:
         super().__init__(filename)
         self.filename = filename
         self.output_filename = filename

libmat2/torrent.py

@@ -2,7 +2,7 @@ from . import abstract
 
 
 class TorrentParser(abstract.AbstractParser):
-    mimetypes = {'application/x-bittorrent', }
+    mimetypes = {b'application/x-bittorrent', }
     whitelist = {b'announce', b'announce-list', b'info'}
 
     def get_meta(self) -> dict: