introduce pyupgrade, run it in python2-compatible mode

.pre-commit-config.yaml

@@ -13,6 +13,10 @@ repos:
     -   id: black
         args: [--line-length=78]
         files: ^src/
+-   repo: https://github.com/asottile/pyupgrade
+    rev: v2.11.0
+    hooks:
+    -   id: pyupgrade
 -   repo: https://github.com/pre-commit/mirrors-mypy
     rev: v0.720
     hooks:

src/flake8/checker.py

@@ -388,7 +388,7 @@ class FileChecker(object):
             # NOTE(sigmavirus24): Historically, pep8 has always reported this
             # as an E902. We probably *want* a better error code for this
             # going forward.
-            message = "{0}: {1}".format(type(e).__name__, e)
+            message = "{}: {}".format(type(e).__name__, e)
             self.report("E902", 0, 0, message)
             return None
 
@@ -476,7 +476,10 @@ class FileChecker(object):
         except (ValueError, SyntaxError, TypeError) as e:
             row, column = self._extract_syntax_information(e)
             self.report(
-                "E999", row, column, "%s: %s" % (type(e).__name__, e.args[0])
+                "E999",
+                row,
+                column,
+                "{}: {}".format(type(e).__name__, e.args[0]),
             )
             return
 

src/flake8/exceptions.py

@@ -40,7 +40,7 @@ class InvalidSyntax(Flake8Exception):
     def __init__(self, exception):  # type: (Exception) -> None
         """Initialize our InvalidSyntax exception."""
         self.original_exception = exception
-        self.error_message = "{0}: {1}".format(
+        self.error_message = "{}: {}".format(
             exception.__class__.__name__, exception.args[0]
         )
         self.error_code = "E902"

src/flake8/plugins/manager.py

@@ -40,7 +40,7 @@ class Plugin(object):
 
     def __repr__(self):  # type: () -> str
         """Provide an easy to read description of the current plugin."""
-        return 'Plugin(name="{0}", entry_point="{1}")'.format(
+        return 'Plugin(name="{}", entry_point="{}")'.format(
             self.name, self.entry_point.value
         )
 

src/flake8/processor.py

@@ -446,7 +446,7 @@ def count_parentheses(current_parentheses_count, token_text):
 def log_token(log, token):  # type: (logging.Logger, _Token) -> None
     """Log a token to a provided logging object."""
     if token[2][0] == token[3][0]:
-        pos = "[%s:%s]" % (token[2][1] or "", token[3][1])
+        pos = "[{}:{}]".format(token[2][1] or "", token[3][1])
     else:
         pos = "l.%s" % token[3][0]
     log.log(

src/flake8/utils.py

@@ -470,7 +470,7 @@ def get_python_version():  # type: () -> str
     :rtype:
         str
     """
-    return "%s %s on %s" % (
+    return "{} {} on {}".format(
         platform.python_implementation(),
         platform.python_version(),
         platform.system(),

tests/unit/test_file_processor.py

@@ -130,7 +130,7 @@ def test_noqa_line_for(default_options):
     ])
 
     for i in range(1, 4):
-        assert file_processor.noqa_line_for(i) == 'Line {0}\n'.format(i)
+        assert file_processor.noqa_line_for(i) == 'Line {}\n'.format(i)
 
 
 def test_noqa_line_for_continuation(default_options):