[Python-Dev] Add more SyntaxWarnings?

[Guido van Rossum]

In this case I agree that a SyntaxWarning is a good idea, per Serhiy's
patch. I would be even more conservative, and only warn if the first object
is a tuple -- the case of the missing comma in the original example appears
likely enough, but I don't expect people to write e.g. `[[1, 2], (3, 4)]`
very often, so leaving the comma out there would be very unlikely.

Regarding the issue of when it's appropriate to issue a SyntaxWarning vs.
when to leave it up to linters, again I would recommend great caution and
only warn about code that is *definitely* going to fail when executed. (Or
at least is *definitely* not going to please the programmer -- one of the
first cases where we added a SyntaxWarning was actually `assert(condition,
message)`, which "fails" by never failing. :-) But this is one of those
cases.

On Thu, Jan 24, 2019 at 2:10 PM Neil Schemenauer <nas-python at arctrix.com>
wrote:

> On 2019-01-24, Terry Reedy wrote:
> > Serhiy Storchaka suggested a compiler SyntaxWarning and uploaded a
> > proof-of-concept diff that handled the above and many similar cases.
>
> I believe that in general we should give better errors or warnings
> if we can do it without huge difficulty.  Serhiy's patch is quite
> simple.  The same check *could* be done by a linting tool.  Putting
> it in CPython will make it more widely available.  These checks
> could be helpful to beginners who probably won't have linting tools
> setup.
>
> I think we should not make it an error, otherwise we have changed
> Python "the language".  We don't want to force other Python
> implementations to do the same check.  It might be hard for them to
> implement.  So, SyntaxWarning seems like a reasonable compromise.
>
> Regards,
>
>   Neil
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-- 
--Guido van Rossum (python.org/~guido)
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