[Python-Dev] Proposed unittest changes (original) (raw)

Steve Holden steve at holdenweb.com
Mon Jul 14 03:06:10 CEST 2008

Tim Peters wrote:

[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. Rats, naturally I was thinking of "if not (a is b):"

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

regards Steve

Steve Holden +1 571 484 6266 +1 800 494 3119 Holden Web LLC http://www.holdenweb.com/

More information about the Python-Dev mailing list