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

PJ Eby pje at telecommunity.com
Tue Sep 29 18:53:07 EDT 2015

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
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