Previously Christian Theune wrote:
> Hi,
>
> Am Montag, den 20.08.2007, 08:59 -0400 schrieb Fred Drake:
> > On 8/20/07, Christian Zagrodnick <[EMAIL PROTECTED]> wrote:
> > > I think we should add a function to validate a given schema on a given
> > > class. This should include constraints and invariants:
> >
> > I do presume you mean object, rather than class, as your example implies.
> >
> > > validateSchema(IMySchema, myobject) [or alike]
> >
> > +1
> >
> > > I'm not sure about return values or exceptions. There are different use
> > > cases:
> > >
> > > 1. Is the object valid? -> True/False
> > > 2. What's wrong with the object -> {attribute/field-name: what's
> > > wrong}, what's wrong with invariants.
> >
> > There should probably be a specific exception that's defined for this
> > purpose, and it could directly support the mapping interface to allow
> > detailed information to be extracted. I suspect a common use would be
> > to simply verify the object and raise the exception in the invalid
> > case, denying whatever operation was being attempted.
> >
> > This also suggests that there's no interesting return value; either
> > the exception is raised or it isn't. Code that wants to introspect
> > the exception can catch that and act accordingly.
>
> >From my latest experience and research of when to use exceptions and
> when to use return values I'd say let's not use an exception.
>
> The report of "which fields are wrong" is the normal result of this
> function. Invalid data is not an uncommon output, rather, it's the sole
> purpose of this function. An exception should be raised if the
> validation could not be performed.
>
> The result could be a structure that lists all errors. Eventually a
> result that equals False could be used to signal no errors, e.g. an
> empty dict or an empty list.
That would be confusing though: I would expect the result of a method
that checks validaty to return something that evaluates to True if
everything is valid. Code like this just messes up my brain:
if not zope.schema.validate(obj, IMySchema):
print "Everything validates correctly!"
to me that is very non-intuitive and looks like the if condition is
incorrect.
Wichert.
--
Wichert Akkerman <[EMAIL PROTECTED]> It is simple to make things.
http://www.wiggy.net/ It is hard to make things simple.
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