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

Chris Angelico rosuav at gmail.com
Mon Feb 8 20:49:50 EST 2016 
On Tue, Feb 9, 2016 at 12:41 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"?

Is assert the *only* statement that has a comma separating unrelated
items? Every other statement that uses a comma is separating identical
items (eg "import os, sys" - "os" and "sys" are equivalent), and
tokens that have completely different meaning are separated by a word.
The only other exception I can think of - pun intended - is the old
"except BaseException, e:" syntax, which got dropped in Py3. Maybe
it's time to introduce a new syntax with a view to deprecating the
comma syntax ("use this old syntax if you need to support Python
2.7").

+1.

ChrisA
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