[PEAK] Default value lost in binding.Obtain()

[PJ Eby]

That's not a typo.  It's part of a strategy to work with multi-part
names.  If the name is a path like 'foo/bar' and acquiring 'foo'
fails, you should not end up with the 'bar' attribute of your default,
which is what would happen with your version.  My version still has a
bug, in that it doesn't work right with *single*-part names, because
the for-loop doesn't execute in that case.  This code really needs
proper tests, but there were apparently never any real tests for this
functionality in the first place.  Most of PEAK's early code was
developed before "test first" and "test-driven" were my standard
practice.  :-(

Anyway, here's a new version that should fix both issues.  I will have
to see about adding some proper tests for this thing and back-testing
to make sure they fail without the patch.


On Sat, Oct 31, 2015 at 3:09 AM, Alexey Smishlayev <alexey at xtech2.lv> wrote:
> It does except for a little typo, at line 60 of the patch it should read "ob
> = acquireComponent(component, attr, default)", then it works good. Thank
> you!
>
>
> Best regards,
> Alexey
>
>
> On 30/10/15 20:59, PJ Eby wrote:
>>
>> Does this patch work for you?
>>
>> On Wed, Oct 28, 2015 at 8:45 AM, Alexey Smishlayev <alexey at xtech2.lv>
>> wrote:
>>>
>>> Hi!
>>> How can I get an svn checkout to incorporate described changes and
>>> propose
>>> another patch? This is essential for our software and I'd like to see it
>>> merged in upstream as soon as possible.
>>>
>>> Best regards,
>>> Alexey
>>>
>>>
>>> On 30/09/15 01:53, PJ Eby wrote:
>>>>
>>>> Thanks for reporting the problem.  Unfortunately your patch will mask
>>>> any other sort of name error, including one that happens indirectly as
>>>> a side effect of the lookup.  I think the correct fix is going to be
>>>> to change the nameNotFound() method of config.IConfigurationRoot to
>>>> include a default (defaulting to NOT_GIVEN), and have
>>>> acquireComponent() take a default and pass it along to nameNotFound().
>>>> This would handle the case of a direct lookup failing by returning the
>>>> default, but still raise an error for any other part of the process
>>>> getting a naming error.
>>>>
>>>> On Tue, Sep 29, 2015 at 9:03 AM, Alexey Smishlayev <alexey at xtech2.lv>
>>>> wrote:
>>>>>
>>>>> Hello!
>>>>>
>>>>> Today, fiddling with the binding.Obtain() I noticed that the default
>>>>> value
>>>>> gets lost.
>>>>>
>>>>> In my application, I have a component tree and I want an attribute to
>>>>> be
>>>>> defined in any component in that tree, so I created binding:
>>>>>
>>>>>>       callback = binding.Obtain("callbackFunction", default=lambda
>>>>>> arg:
>>>>>> None)
>>>>>>
>>>>> So, in case that no component defines a callbackFunction, the lambda
>>>>> function would be used as a fallback.
>>>>> Unfortunately, "default" option is ignored unless target name contains
>>>>> slashes (e.g. "/callbackFunction", "./callBackFunction",
>>>>> "../callbackFunction")
>>>>>
>>>>> I went to the peak/binding/components.py trying to fix it and propose
>>>>> the
>>>>> attached patch.
>>>>> The problem is that default value was not propagated to the
>>>>> acquireComponent() call, so an exception occurred.
>>>>>
>>>>>
>>>>> Best regards,
>>>>> Alexey Smishlayev
>>>>>
>>>>> _______________________________________________
>>>>> PEAK mailing list
>>>>> PEAK at eby-sarna.com
>>>>> http://www.eby-sarna.com/mailman/listinfo/peak
>>>
>>>
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>
>
>
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