Small lint of expression.py

Author: rocky

mathics/core/expression.py

@@ -2,11 +2,9 @@
 # cython: language_level=3
 # -*- coding: utf-8 -*-
 
-import ast
 import sympy
 import mpmath
 import math
-import inspect
 import re
 
 import typing
@@ -141,7 +139,7 @@ def from_python(arg):
 
 class KeyComparable(object):
     def get_sort_key(self):
-        raise NotImplemented
+        raise NotImplementedError
 
     def __lt__(self, other) -> bool:
         return self.get_sort_key() < other.get_sort_key()
@@ -381,7 +379,7 @@ def do_format(self, evaluation, form):
             leaves = self.get_leaves()
             include_form = False
             # If the expression is enclosed by a Format
-            # takes the form from the expression and 
+            # takes the form from the expression and
             # removes the format from the expression.
             if head in formats and len(leaves) == 1:
                 expr = leaves[0]
@@ -432,7 +430,7 @@ def format_expr(expr):
                     if result is not None and result != expr:
                         return result.evaluate(evaluation)
                 return None
-            
+
             formatted = format_expr(expr)
             if formatted is not None:
                 result = formatted.do_format(evaluation, form)