E714: fix chained is not

Closes #767

Author: Susannah Klaneček

pycodestyle.py

@@ -140,7 +140,8 @@ def lru_cache(maxsize=128):  # noqa as it's a fake implementation.
 WHITESPACE_AFTER_COMMA_REGEX = re.compile(r'[,;:]\s*(?:  |\t)')
 COMPARE_SINGLETON_REGEX = re.compile(r'(\bNone|\bFalse|\bTrue)?\s*([=!]=)'
                                      r'\s*(?(1)|(None|False|True))\b')
-COMPARE_NEGATIVE_REGEX = re.compile(r'\b(not)\s+[^][)(}{ ]+\s+(in|is)\s')
+COMPARE_NEGATIVE_REGEX = re.compile(r'\b(not)\s+[^][)(}{ ]+\s+(in|is)'
+                                    r'\s+(?!not\s)')
 COMPARE_TYPE_REGEX = re.compile(r'(?:[=!]=|is(?:\s+not)?)\s+type(?:s.\w+Type'
                                 r'|\s*\(\s*([^)]*[^ )])\s*\))')
 KEYWORD_REGEX = re.compile(r'(\s*)\b(?:%s)\b(\s*)' % r'|'.join(KEYWORDS))

testsuite/E71.py

@@ -64,6 +64,9 @@
 #: E714
 if not X.B is Y:
     pass
+#: E714
+if not X is Y is not Z:
+    pass
 
 #
 #: Okay
@@ -79,6 +82,9 @@
 if x is not y:
     pass
 
+if X is not Y is not Z:
+    pass
+
 if TrueElement.get_element(True) == TrueElement.get_element(False):
     pass