[Python-ideas] Displaying DeprecationWarnings in the interactive interpreter, second try

[Ian Cordasco]

On Wed, May 27, 2015 at 7:29 PM, Nathaniel Smith <njs at pobox.com> wrote:
> Hi all,
>
> I'm tired of getting bug reports like this one:
>
>   https://github.com/numpy/numpy/issues/5919
>
> where the issue is just that the user didn't see deprecation warnings,
> so I just filed a bug report requesting that the interactive Python
> REPL start printing DeprecationWarnings when users use deprecated
> functionality:
>
>   https://bugs.python.org/issue24294
>
> In the bug report it was pointed out that this was discussed on
> python-ideas a few months ago, and the discussion petered out without
> any consensus:
>
>   http://thread.gmane.org/gmane.comp.python.ideas/32191
>
> As far as I can tell, though, there were only two real objections
> raised in that previous thread, and IMO neither is really convincing.
> So let me pre-empt those now:
>
> Objection 1: This will cause the display of lots of unrelated warnings.
>
> Response: You misunderstand the proposal. I'm not suggesting that we
> display *all* DeprecationWarnings whenever the interactive interpreter
> is running; I'm only suggesting that we display the deprecation
> warnings that are warning about *code that was actually typed at the
> interpreter*.
>
> # not this
> warnings.filterwarnings("default", category=DeprecationWarning)
>
> # this
> warnings.filterwarnings("default", category=DeprecationWarning,
> module="__main__")
>
> So for example, if we have
>
> # module1.py
> def deprecated_function():
>     warnings.warn("stop it!", DeprecationWarning, stacklevel=2)
>
> # module2.py
> import module1
> def foo():
>     module1.deprecated_function()
>
>>> import module1, module2
> # This doesn't print a warning, because 'foo' is not deprecated
> # it merely uses deprecated functionality, which is not my problem,
> # because I am merely a user of module1, not the author.
>>> module2.foo()
> # This *does* print a warning, because now I am using the
> # deprecated functionality directly.
>>> module1.deprecated_function()
> __main__:1: DeprecationWarning: stop it!
>
>
> Objection 2: There are lots of places that code is run interactively
> besides the standard REPL -- there's IDLE and IPython and etc.
>
> Response: Well, this isn't really an objection :-). Basically I'm
> looking for consensus from the CPython team that this is what should
> happen in the interactive interpreters that they distribute. Other
> interfaces can then follow that lead or not. (For some value of
> "follow". By the time you read this IPython may have already made the
> change: https://github.com/ipython/ipython/pull/8480 ;-).)
>
> So, totally awesome idea, let's do it, yes/yes?
>
> -n
>
> --
> Nathaniel J. Smith -- http://vorpus.org
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I'm in favor of this. It's especially convincing to me that IPython is
considering a similar change.