[lazy_extractors] Fix suitable and add flake8 test

yt_dlp/extractor/common.py

@@ -458,6 +458,8 @@ class InfoExtractor(object):
     @classmethod
     def suitable(cls, url):
         """Receives a URL and returns True if suitable for this IE."""
+        # This function must import everything it needs (except other extractors),
+        # so that lazy_extractors works correctly
         return cls._match_valid_url(url) is not None
 
     @classmethod
@@ -622,7 +624,7 @@ class InfoExtractor(object):
     @classmethod
     def ie_key(cls):
         """A string for getting the InfoExtractor with get_info_extractor"""
-        return compat_str(cls.__name__[:-2])
+        return cls.__name__[:-2]
 
     @property
     def IE_NAME(self):

yt_dlp/extractor/rutube.py

@@ -297,6 +297,8 @@ class RutubePlaylistIE(RutubePlaylistBaseIE):
 
     @classmethod
     def suitable(cls, url):
+        from ..utils import int_or_none, parse_qs
+
         if not super(RutubePlaylistIE, cls).suitable(url):
             return False
         params = parse_qs(url)

yt_dlp/extractor/youtube.py

@@ -1837,8 +1837,6 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
 
     @classmethod
     def suitable(cls, url):
-        # Hack for lazy extractors until more generic solution is implemented
-        # (see #28780)
         from ..utils import parse_qs
 
         qs = parse_qs(url)