Cleanup the _warnings module

skimage/_shared/_warnings.py

@@ -1,11 +1,11 @@
-__all__ = ['all_warnings', 'expected_warnings']
-
 from contextlib import contextmanager
 import sys
 import warnings
 import inspect
 import re
 
+__all__ = ['all_warnings', 'expected_warnings', 'warn']
+
 
 def warn(message, category=None, stacklevel=2):
     """A version of `warnings.warn` with a default stacklevel of 2.
@@ -98,7 +98,8 @@ def expected_warnings(matching):
     that may produce different warnings.  The behaviors can be combined.
     If you pass multiple patterns, you get an orderless "and", where all of the
     warnings must be raised.
-    If you use the "|" operator in a pattern, you can catch one of several warnings.
+    If you use the "|" operator in a pattern, you can catch one of several
+    warnings.
     Finally, you can use "|\A\Z" in a pattern to signify it as optional.
 
     """
@@ -106,7 +107,7 @@ def expected_warnings(matching):
         # enter context
         yield w
         # exited user context, check the recorded warnings
-        remaining = [m for m in matching if not '\A\Z' in m.split('|')]
+        remaining = [m for m in matching if '\A\Z' not in m.split('|')]
         for warn in w:
             found = False
             for match in matching: