[Python-Dev] Issue #26204: compiler now emits a SyntaxWarning on constant statement

[Guido van Rossum]

On Mon, Feb 8, 2016 at 5:41 PM, MRAB <python at mrabarnett.plus.com> wrote:
> On 2016-02-09 00:53, Guido van Rossum wrote:
>>
>> The warning for 'assert (cond, msg)' was specifically put in because
>> this is a nasty trap. It's *always* a mistaken attempt to write
>> 'assert cond, msg' -- usually in an attempt to break a long line
>> without using a backslash. I'd actually consider promoting it to a
>> syntax error rather than removing the warning.
>>
>> Compared to other "lint warnings" this one is much nastier -- it is
>> also much more certain that it is a mistake. (Much more certain than
>> e.g. an undefined variable, which could still be legitimate code due
>> to dynamic updates to globals() or builtins.)
>
> Would there be less chance of confusion if there were some kind of syntax
> such as "assert cond with msg"?

Perhaps, but as long as the "with msg" isn't mandatory and the "assert
x, y" syntax is still valid we'd still have to warn about "assert (x,
y)". Note that in general "assert constant" is not a problem (assert
True and assert False have their uses :-). It's only the literal tuple
form.

-- 
--Guido van Rossum (python.org/~guido)