Fixed multiple problems related to migration to django-preferences.

app/YtManagerApp/utils/__init__.py

@@ -1,9 +1,9 @@
 
 def first_non_null(*iterable):
-    '''
+    """
     Returns the first element from the iterable which is not None.
     If all the elements are 'None', 'None' is returned.
     :param iterable: Iterable containing list of elements.
     :return: First non-null element, or None if all elements are 'None'.
-    '''
+    """
     return next((item for item in iterable if item is not None), None)

app/YtManagerApp/utils/subscription_file_parser.py

@@ -1,4 +1,4 @@
-from typing import Iterable
+from typing import Iterable, Optional
 from xml.etree import ElementTree
 import re
 
@@ -12,7 +12,7 @@ class SubFileParser(object):
     def probe(self, file_handle) -> bool:
         """
         Tests if file matches file format.
-        :param file: File path
+        :param file_handle: File handle
         :return: True if file matches, false otherwise
         """
         return False
@@ -20,7 +20,7 @@ class SubFileParser(object):
     def parse(self, file_handle) -> Iterable[str]:
         """
         Parses file and returns a list of subscription URLs.
-        :param file:
+        :param file_handle:
         :return:
         """
         return []
@@ -63,7 +63,7 @@ class OPMLParser(SubFileParser):
     """
     def __init__(self):
         self.__cached_file = None
-        self.__cached_tree: ElementTree.ElementTree = None
+        self.__cached_tree: Optional[ElementTree.ElementTree] = None
 
     def __parse(self, file_handle):
         if file_handle == self.__cached_file:

app/YtManagerApp/utils/youtube.py

@@ -7,8 +7,8 @@ class YoutubeAPI(YouTube):
 
     @staticmethod
     def build_public() -> 'YoutubeAPI':
-        from YtManagerApp.management.appconfig import youtube_api_key
-        return YoutubeAPI(key=youtube_api_key)
+        from YtManagerApp.management.appconfig import appconfig
+        return YoutubeAPI(key=appconfig.youtube_api_key)
 
     # @staticmethod
     # def build_oauth() -> 'YoutubeAPI':