Improve a few mypy type annotations

src/flake8/checker.py

@@ -5,7 +5,7 @@ import logging
 import signal
 import sys
 import tokenize
-from typing import List, Optional
+from typing import List, Optional, Tuple
 
 try:
     import multiprocessing
@@ -247,7 +247,7 @@ class Manager(object):
         LOG.info("Checking %d files", len(self.checkers))
 
     def report(self):
-        # type: () -> (int, int)
+        # type: () -> Tuple[int, int]
         """Report all of the errors found in the managed file checkers.
 
         This iterates over each of the checkers and reports the errors sorted

src/flake8/main/application.py

@@ -4,7 +4,7 @@ from __future__ import print_function
 import logging
 import sys
 import time
-from typing import List, Optional, Sequence
+from typing import List, Optional
 
 import flake8
 from flake8 import checker
@@ -99,6 +99,7 @@ class Application(object):
         self.parsed_diff = {}
 
     def parse_preliminary_options_and_args(self, argv=None):
+        # type: (Optional[List[str]]) -> None
         """Get preliminary options and args from CLI, pre-plugin-loading.
 
         We need to know the values of a few standard options and args now, so
@@ -347,7 +348,7 @@ class Application(object):
         self.formatter.show_statistics(self.guide.stats)
 
     def initialize(self, argv):
-        # type: (Sequence[str]) -> None
+        # type: (Optional[List[str]]) -> None
         """Initialize the application to be run.
 
         This finds the plugins, registers their options, and parses the

src/flake8/utils.py

@@ -8,8 +8,8 @@ import platform
 import re
 import sys
 import tokenize
-from typing import Callable, Dict, Generator, List, Pattern, Sequence, Tuple
-from typing import Union
+from typing import Callable, Dict, Generator, List, Pattern, Sequence, Set
+from typing import Tuple, Union
 
 from flake8 import exceptions
 
@@ -217,7 +217,7 @@ def stdin_get_value():
 
 
 def parse_unified_diff(diff=None):
-    # type: (str) -> List[str]
+    # type: (str) -> Dict[str, Set[int]]
     """Parse the unified diff passed on stdin.
 
     :returns: