On Wednesday, November 30, 2011 5:16:59 PM UTC-5, lyn2py wrote:
>
> Thanks Anthony.
>
> That's interesting syntax to use a validator!
>
Well, the validators are mostly intended to be used for validating form
fields. They are callable objects, so you instantiate a validator like
IS_SLUG(), which is an object with a __call__ method that takes a value and
validates it. The __call__ method returns a tuple, which is the (possibly
transformed) value and either an error message or None. A few of the
validators, such as IS_SLUG, actually transform the input value rather than
simply checking it, so they can also be used independently for their
transformation effects. Of course, in that case, the required syntax seems
a bit awkward:
IS_SLUG() # creates a callable object - usually passed as the 'requires'
arg to Field()
IS_SLUG()('My Title') # passes a value to the __call__ method of the
validator object
IS_SLUG()('My Title')[0] # extracts the returned value, which is the first
element of the returned tuple
To make it easier, you can write your own helper:
make_slug = lambda v: IS_SLUG()(v)[0]
Then do:
title_slug = make_slug('My Title')
This is like Bruno's compute example. You could also make a more general
helper that works with any validator:
>>> transform = lambda v, validator: validator()(v)[0]
>>> transform('my title', IS_SLUG)
'my-title'
>>> transform('My Title', IS_UPPER)
'MY TITLE'
Anthony
