Run flake8

`devscripts/buildserver.py` is too broken for me to bother with

setup.cfg

@@ -2,7 +2,7 @@
 universal = True
 
 [flake8]
-exclude = build,venv,.tox,.git,.pytest_cache
+exclude = build,venv,.tox,.git,.pytest_cache,devscripts/buildserver.py
 ignore = E402,E501,E731,E741,W503
 max_line_length = 80
 per_file_ignores =

setup.py

@@ -18,7 +18,7 @@ from distutils.spawn import spawn
 try:
     # This will create an exe that needs Microsoft Visual C++ 2008
     # Redistributable Package
-    import py2exe
+    import py2exe  # noqa: F401
 except ImportError:
     if len(sys.argv) >= 2 and sys.argv[1] == 'py2exe':
         print('Cannot import py2exe', file=sys.stderr)
@@ -42,11 +42,11 @@ LONG_DESCRIPTION = 'Command-line program to download videos from YouTube.com and
 py2exe_console = [{
     'script': './youtube_dl/__main__.py',
     'dest_base': 'youtube-dl',
-    'version': __version__,
+    'version': __version__,  # noqa: F821
     'description': DESCRIPTION,
     'comments': LONG_DESCRIPTION,
     'product_name': 'youtube-dl',
-    'product_version': __version__,
+    'product_version': __version__,  # noqa: F821
 }]
 
 py2exe_params = {
@@ -103,7 +103,7 @@ class build_lazy_extractors(Command):
 
 setup(
     name='youtube_dl',
-    version=__version__,
+    version=__version__,  # noqa: F821
     description=DESCRIPTION,
     long_description=LONG_DESCRIPTION,
     url='https://github.com/ytdl-org/youtube-dl',

youtube_dl/extractor/__init__.py

@@ -1,19 +1,19 @@
 from __future__ import unicode_literals
 
 try:
-    from .lazy_extractors import *
+    from .lazy_extractors import *  # noqa: F403
     from .lazy_extractors import _ALL_CLASSES
     _LAZY_LOADER = True
 except ImportError:
     _LAZY_LOADER = False
-    from .extractors import *
+    from .extractors import *  # noqa: F403
 
     _ALL_CLASSES = [
         klass
         for name, klass in globals().items()
         if name.endswith('IE') and name != 'GenericIE'
     ]
-    _ALL_CLASSES.append(GenericIE)
+    _ALL_CLASSES.append(GenericIE)  # noqa: F405
 
 
 def gen_extractor_classes():