Re: overriding validate_python (and similar methods) in validators

(catching up on emails I forgot about)

Jacob Smullyan wrote:
> Hello.  I'm a bit new to FormEncode, so pardon me if I'm bringing up
> an old chestnut or need to be set straight about something.
> 
> I recently had a bunch of custom validators, subclassing
> FancyValidator or one of its subclasses (Regex, for instance), and
> then I found a bug in one of them -- I overrode validate_python but
> didn't call the same method on the superclass, so didn't get the
> complete validation.  (I believe this was a Regex subclass.)  So I
> went through my validators and made sure that whenever I wrote a
> validate_python method, I called the corresponding superclass method.
> Then I tried running it, and whoah!  for some but not all of the
> validators, this gave rise to an error, because validate_python in
> FancyValidator is None.
> 
> I take it that the reason FormEncode allows validate_python et al to
> have the value of None is to support a declarative programming style.
> But to my mind the use of this feature in FancyValidator, a base
> class, makes the interface it presents rather confusing and
> unpredictable, and, I think, results in an excessively leaky
> abstraction.  Couldn't these methods be defined there as noops, or
> would that have side-effects I'm unaware of?

It's purely for efficiency, so if the method isn't defined it doesn't 
get called.  It's really only meant to be called from 
FancyValidator.(to|from)_python.  Though now that you mention it, 
there's no very good way to tell the difference between a validator that 
overrides this method (and hence you have to call the superclass), and 
one that doesn't (and hence you can't call the superclass).

I've changed this in the trunk.

-- 
Ian Bicking | [email protected] | http://blog.ianbicking.org

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