[Michael Foord]
... Adding the following new asserts:
... assertNotIs (first, second, msg=None)
[Steve Holden]
Please, let's call this one "assertIsNot".
+1
I know it's valid Python to say
if a not is b:
Nope, that's a syntax error.
but it's a much less natural way of expressing the condition, and (for all I know) might even introduce an extra negation operation. "is not" is, I believe, treated as a single operator.
"is not" and "not in" are both binary infix operators, not to be confused with the distinct use of "not" on its own as a unary prefix operator. "not is" and "in not" are both gibberish.
1 is not 2 True 1 is (not 2) False 1 not is 2 SyntaxError: invalid syntax
1 not in [2] True 1 in not [2] SyntaxError: invalid syntax 1 in (not [2]) Traceback (most recent call last): ... TypeError: argument of type 'bool' is not iterable