Allow custom template tags to accept keyword only arguments

[Alexander Allakhverdiyev]

Example tag with a keyword-only argument

@register.simple_tag(takes_context=True)
def my_tag(context, arg1, *, kwarg2='n/a'):
    return ''

Html code

<div>bla bla bla</div>
{% my_tag 'arg_1_value' kwarg_2='kwarg_value' %}

Result

django.template.exceptions.TemplateSyntaxError: 'my_tag' received unexpected keyword argument 'kwarg_2'

[Alexander Allakhverdiyev]

Also we no longer need to use custom django.utils.inspect.getargspec anymore and can switch to python's ​inspect.getfullargspec()

[Tim Graham]

​PR

[Tim Graham]

Based on my understanding of ​the Python issue, I don't think we want to use ​inspect.getfullargspec() as this is a discouraged API that may be removed at some point.

[Alexander Allakhverdiyev]

It was deprecated in python 3.5, but they had changed their mind in 3.6

Check out the description of this function specifically for 3.6 (and 3.7dev too)
​https://docs.python.org/3.6/library/inspect.html#inspect.getfullargspec

Changed in version 3.6: This method was previously documented as deprecated in favour of signature() in Python 3.5, but that decision has been reversed in order to restore a clearly supported standard interface for single-source Python 2/3 code migrating away from the legacy getargspec() API.

Based on that discussion they might want to deprecate it at some point in the future. But personally, I don't think that's a good enough reason to have a complete re-implementation of the function.

[Tim Graham]

Okay, ​Nick confirmed that getfullargspec() won't be deprecated in the future. Could you submit a separate PR to replace django.utils.inspect.getargspec() with it? You can rebase the patch for this ticket after that's completed.

[Alexander Allakhverdiyev]

Okay, thank you! I've submitted ​PR#8428 to use inspect.getfullargspec() and rebased the patch.

[Tim Graham <timograham@…>]

In a7c6c70:

Fixed #28129 -- Allowed custom template tags to use keyword-only arguments.