[Python-Dev] Re: Changing exception text in micro releases

[Serhiy Storchaka]

24.09.21 16:51, Eric V. Smith пише:
> This is clearly an improvement. My question is: is it okay to backport
> this to 3.9 and 3.10? I think we have a rule that it's okay to change
> the exception text, but I'm not sure how that applies to micro releases
> (3.9.x, 3.10.1).

I am sure that it will break someone's tests. Since the current error
message is not wrong, it is not a bug fix.

If you want it very much you can discuss backporting to 3.10.1 with
Pablo. Few people will upgrade immediately after releasing 3.10.0, and
for others this change will be a part of upgrading to 3.10. But 3.9 is
mature enough for now.

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[Python-Dev] Re: Changing exception text in micro releases

[Eric V. Smith]

On 9/24/2021 4:53 PM, Guido van Rossum wrote:

In this case I am inclined not to backport.

I agree. I decided not to backport it.
In general we should look at existing usage before making changes. 
Somebody’s code might break — but does it matter? That depends on a 
lot of factors. E.g. if parsing an error message has become a common 
way to get useful info out of the error that is not easily available 
otherwise, we have to tread lightly.


In this case I don't think anyone could be parsing it, because the 
existing version doesn't contain any information, it's always the string 
"Invalid format specifier". But I agree we should be cautious, so this 
will wait until 3.11. The original bug was reported 7.5 years ago, so 
it's not like we're in any rush.


Thanks for the input.

Eric



—Guido

On Fri, Sep 24, 2021 at 09:59 Terry Reedy > wrote:


On 9/24/2021 10:46 AM, Eric V. Smith wrote:
> On 9/24/2021 10:39 AM, Ethan Furman wrote:
>> On 9/24/21 6:51 AM, Eric V. Smith wrote:
>>
>>
>> > This is clearly an improvement. My question is: is it okay to
>> backport this to 3.9 and 3.10? I
>> > think we have a rule that it's okay to change the exception
text,
>> but I'm not sure how that
>> > applies to micro releases (3.9.x, 3.10.1).
>>
>> "better" != "bug fix", so I wouldn't change it in a micro release.
>
> Yeah, as much as I'd love to see this included, you're right.
Thanks for
> the "adult" take on it.

Exception messages are subject to change in each new version, without
deprecating the old version.  Changes are sometimes backported
when the
existing message is sufficiently erroneous. 'Sufficiently' means
something like 'harm of error outweighs harm of changing'. I don't
think a simple, easily recognized, typo or grammar error qualifies.
Among active developers, I believe Guido has the most continuity of
experience with such discussions and decisions.  Perhaps something
could
usefully be added to the devguide, but I am not sure.


-- 
Terry Jan Reedy


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--Guido (mobile)

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[Python-Dev] Re: Changing exception text in micro releases

[Guido van Rossum]

In this case I am inclined not to backport.

In general we should look at existing usage before making changes.
Somebody’s code might break — but does it matter? That depends on a lot of
factors. E.g. if parsing an error message has become a common way to get
useful info out of the error that is not easily available otherwise, we
have to tread lightly.

—Guido

On Fri, Sep 24, 2021 at 09:59 Terry Reedy  wrote:

> On 9/24/2021 10:46 AM, Eric V. Smith wrote:
> > On 9/24/2021 10:39 AM, Ethan Furman wrote:
> >> On 9/24/21 6:51 AM, Eric V. Smith wrote:
> >>
> >>
> >> > This is clearly an improvement. My question is: is it okay to
> >> backport this to 3.9 and 3.10? I
> >> > think we have a rule that it's okay to change the exception text,
> >> but I'm not sure how that
> >> > applies to micro releases (3.9.x, 3.10.1).
> >>
> >> "better" != "bug fix", so I wouldn't change it in a micro release.
> >
> > Yeah, as much as I'd love to see this included, you're right. Thanks for
> > the "adult" take on it.
>
> Exception messages are subject to change in each new version, without
> deprecating the old version.  Changes are sometimes backported when the
> existing message is sufficiently erroneous. 'Sufficiently' means
> something like 'harm of error outweighs harm of changing'.  I don't
> think a simple, easily recognized, typo or grammar error qualifies.
> Among active developers, I believe Guido has the most continuity of
> experience with such discussions and decisions.  Perhaps something could
> usefully be added to the devguide, but I am not sure.
>
>
> --
> Terry Jan Reedy
>
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>
-- 
--Guido (mobile)
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[Python-Dev] Re: Changing exception text in micro releases

[Terry Reedy]

On 9/24/2021 10:46 AM, Eric V. Smith wrote:

On 9/24/2021 10:39 AM, Ethan Furman wrote:

On 9/24/21 6:51 AM, Eric V. Smith wrote:


> This is clearly an improvement. My question is: is it okay to 
backport this to 3.9 and 3.10? I
> think we have a rule that it's okay to change the exception text, 
but I'm not sure how that

> applies to micro releases (3.9.x, 3.10.1).

"better" != "bug fix", so I wouldn't change it in a micro release.


Yeah, as much as I'd love to see this included, you're right. Thanks for 
the "adult" take on it.


Exception messages are subject to change in each new version, without 
deprecating the old version.  Changes are sometimes backported when the 
existing message is sufficiently erroneous. 'Sufficiently' means 
something like 'harm of error outweighs harm of changing'.  I don't 
think a simple, easily recognized, typo or grammar error qualifies. 
Among active developers, I believe Guido has the most continuity of 
experience with such discussions and decisions.  Perhaps something could 
usefully be added to the devguide, but I am not sure.



--
Terry Jan Reedy

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[Python-Dev] Re: Changing exception text in micro releases

[Eric V. Smith]

On 9/24/2021 10:39 AM, Ethan Furman wrote:

On 9/24/21 6:51 AM, Eric V. Smith wrote:


> This is clearly an improvement. My question is: is it okay to 
backport this to 3.9 and 3.10? I
> think we have a rule that it's okay to change the exception text, 
but I'm not sure how that

> applies to micro releases (3.9.x, 3.10.1).

"better" != "bug fix", so I wouldn't change it in a micro release.


Yeah, as much as I'd love to see this included, you're right. Thanks for 
the "adult" take on it.


Eric


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[Python-Dev] Re: Changing exception text in micro releases

[Ethan Furman]

On 9/24/21 6:51 AM, Eric V. Smith wrote:


> This is clearly an improvement. My question is: is it okay to backport this 
to 3.9 and 3.10? I
> think we have a rule that it's okay to change the exception text, but I'm not 
sure how that
> applies to micro releases (3.9.x, 3.10.1).

"better" != "bug fix", so I wouldn't change it in a micro release.

--
~Ethan~
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[Python-Dev] Re: Changing exception text in micro releases

[Filipe Laíns]

On Fri, 2021-09-24 at 09:51 -0400, Eric V. Smith wrote:
> This PR https://github.com/python/cpython/pull/28310 changes the message 
> for some exceptions.
> 
> Currently:
> 
>  >>> format('', '%M')
> Traceback (most recent call last):
>    File "", line 1, in 
> ValueError: Invalid format specifier
> 
> With the proposed change:
>  >>> format('', '%M')
> Traceback (most recent call last):
>    File "", line 1, in 
> ValueError: Invalid format specifier '%M' for object of type 'str'
> 
> This also applies to str.format() and f-strings.
> 
> This is clearly an improvement. My question is: is it okay to backport 
> this to 3.9 and 3.10? I think we have a rule that it's okay to change 
> the exception text, but I'm not sure how that applies to micro releases 
> (3.9.x, 3.10.1).
> 
> Eric

People might be depending on the exception text. Tests would probably be the
most relevant example. OTOH, the breakage shouldn't be that big, and probably
depending on exception strings in situations like this is not great.

If we are being safe, I'd probably avoid it.

According to the devguide[1], micro versions are bugfixes releases, which this
is not, so I'd say the patch should not be backported.

However, I don't know if there is maybe another guideline or precedent.

[1] https://devguide.python.org/devcycle

Cheers,
Filipe Laíns


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