Incorrect `validator` docs

[leebenson]

I spent about an hour trying to implement a custom validator per http://docs.python-cerberus.org/en/stable/customize.html, and finally realised that the docs are wrong!

This:

class MyValidator(Validator):
    def _validate_isodd(self, isodd, field, value):

should be:

class MyValidator(Validator):
    def _validator_isodd(self, isodd, field, value):

i.e. _validate_ -> _validator_

[funkyfuture]

disclaimer: i might be wrong as i'm quiet tired.

the _validate_-prefix is used for custom rules (isodd in the example) while _validator_ is for the validator rule (which doesn't require to subclass Validator, but does't allow to define constraints in schemas). if i'm not wrong, it nonetheless raises the point that the documentation should be more verbose on that difference. contributions in this regard are highly appreciated!

[leebenson]

Thanks - makes sense @funkyfuture. I agree that the docs could do with a clarification- it definitely wasn't obvious to me that _validator_ and _validate_ were two different concepts.

[funkyfuture]

i pledge to mark this for the 1.2 milestone.

[bryanwweber]

FWIW, I also asked a question on StackOverflow about this topic: https://stackoverflow.com/q/39438774/2449192 @nicolaiarocci Answered me there as well, but I didn't quite understand his answer.

[funkyfuture]

@bryanwweber, i edited Nicola's answer yesterday or the day before to point a major difference. i notice, i should amend an example (put a link to one now). if there's still clarification needed, please let us know.

one thought: maybe we shouldn't talk of 'custom validators', there are no standard ones, so custom rule vs. validator.