On Thu, Sep 2, 2021 at 7:36 PM Peter Otten <__pete...@web.de> wrote:
>
> On 02/09/2021 04:32, Steven D'Aprano wrote:
> > On Wed, Sep 01, 2021 at 03:40:37PM +0200, Peter Otten wrote:
> >
> >> Instead of removing it you might add a filter to get a similar effect:
> >
> > [...]
> >
> >>>>> warnings.filterwarnings("always", "woof!")
> >
> > Unfortunately that's too aggressive. In my use-case, `bark` will be
> > called many, many times in a loop, and so potentially "woof" will be
> > displayed over and over again. That will be annoying.
> >
> > Once it has been displayed *once* in that loop, it shouldn't be
> > displayed again for the rest of the loop.
> >
> > Also, `bark` is being called from a comprehension or sort key
> > function, so it is difficult to keep an explicit flag myself:
> >
> > # My use case is *not* this
> > def process(values):
> > seen = False
> > for item in values:
> > if condition:
> > if seen: bark()
> > seen = True
> >
> > # More like this:
> > sorted(values, key=func) # func may call bark
> >
> >
> > Allowing `bark` to *always* display could be annoying. Ideally I want it
> > to be displayed *at most* once per call to sorted(). I can do that by
> > removing the filter after sorting. Or at least I could if it were
> > possible to remove individual filters.
>
> Then use filterwarnings("once", ...):
>
> >>> import warnings
> >>> def bark():
> warnings.warn("woof!")
>
>
> >>> for i in range(6):
> print(i)
> if i == 3: warnings.filterwarnings("once", "woof!")
> bark()
>
>
> 0
>
> Warning (from warnings module):
> File "<pyshell#145>", line 2
> UserWarning: woof!
> 1
> 2
> 3
>
> Warning (from warnings module):
> File "<pyshell#145>", line 2
> UserWarning: woof!
> 4
> 5
>
> For good performance you'd ideally provide the lineno, but I don't see a
> clean way to get that.
>
That has the side effect that all OTHER warnings get their onceness
reset too though.
>>> warnings.warn("hello")
<stdin>:1: UserWarning: hello
>>> warnings.warn("world")
<stdin>:1: UserWarning: world
>>> warnings.warn("hello")
>>> warnings.warn("world")
>>> warnings.filterwarnings("once", "hello")
>>> warnings.warn("hello")
<stdin>:1: UserWarning: hello
>>> warnings.warn("world")
<stdin>:1: UserWarning: world
(It's actually the same as resetfilters, and for the same reason -
whenever the filters change, all oncenesses get forgotten.)
ChrisA
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