Fix static analysis errors in IPython.core.formatters

Closes gh-7054

IPython/core/formatters.py

@@ -13,6 +13,7 b' Inheritance diagram:'
 import abc
 import inspect
 import sys
+import traceback
 import types
 import warnings
 
@@ -229,7 +230,7 b' def warn_format_error(method, self, *args, **kwargs):'
     """decorator for warning on failed format call"""
     try:
         r = method(self, *args, **kwargs)
-    except NotImplementedError as e:
+    except NotImplementedError:
         # don't warn on NotImplementedErrors
         return None
     except Exception: