A better way to suppress unused import warnings

setup.cfg

@@ -11,8 +11,3 @@ docs = easy_install zope.exceptions[docs]
 
 [bdist_wheel]
 universal = 1
-
-[flake8]
-extend-ignore = F401
-# https://pep8.readthedocs.org/en/latest/intro.html#error-codes
-# F401: ``module`` imported but unused

src/zope/exceptions/__init__.py

@@ -26,9 +26,15 @@
 from zope.exceptions.exceptionformatter import print_exception
 from zope.exceptions.exceptionformatter import extract_stack
 
+__all__ = [
+    'DuplicationError', 'IDuplicationError', 'UserError', 'IUserError',
+    'format_exception', 'print_exception', 'extract_stack',
+]
+
+
 # avoid dependency on zope.security:
 try:
-    import zope.security
+    import zope.security  # noqa: suppress unused import warning from flake8
 except ImportError as v:  # pragma: no cover
     # "ImportError: No module named security"
     if 'security' not in str(v):
@@ -40,3 +46,7 @@
     from zope.security.interfaces import IForbiddenAttribute
     from zope.security.interfaces import Forbidden
     from zope.security.interfaces import ForbiddenAttribute
+    __all__ += [
+        'IUnauthorized', 'Unauthorized', 'IForbidden', 'IForbiddenAttribute',
+        'Forbidden', 'ForbiddenAttribute',
+    ]

src/zope/exceptions/exceptionformatter.py

@@ -174,7 +174,8 @@ def formatLastLine(self, exc_line):
         return self.escape(exc_line)
 
     def formatException(self, etype, value, tb):
-        # The next line provides a way to detect recursion.
+        # The next line provides a way to detect recursion.  The 'noqa'
+        # comment disables a flake8 warning about the unused variable.
         __exception_formatter__ = 1  # noqa
         result = []
         while tb is not None:
@@ -206,7 +207,8 @@ def extractStack(self, f=None):
             except ZeroDivisionError:
                 f = sys.exc_info()[2].tb_frame.f_back
 
-        # The next line provides a way to detect recursion.
+        # The next line provides a way to detect recursion.  The 'noqa'
+        # comment disables a flake8 warning about the unused variable.
         __exception_formatter__ = 1  # noqa
         result = []
         while f is not None: