Colander: Is preparer supported in schema binding? - pylons-discuss

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Message from discussion Colander: Is preparer supported in schema binding?
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Date: Sun, 13 Nov 2011 13:28:25 -0300
From: Mariano Mara <mariano.m...@gmail.com>
To: pylons-discuss@googlegroups.com
Subject: Re: Colander: Is preparer supported in schema binding?
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On 11.11.11 18:48, Chris Withers wrote:
> On 10/11/2011 17:57, Mariano Mara wrote:
> >
> >I even ran the tests and it worked ok (and my problem seems to be fixed too).
> >It would be great if somebody with great colander jutsu can say  why such
> >behavior was not implemented.
> 
> I implemented the feature, but I don't used deferreds.
> (I didn't like the idea myself, but that doesn't mean they're bad...)
> 
> I also have my finger in the xlrd pie, and personally I wish xlrd
> would just create date objects on parsing the .xls rather than the
> annoying number-you-need-to-bend-over-backwards-to-turn-into-a-date
> ;-)
> 
> Why not just store the book *and* the preparer as attributes of the
> Schema instance, then they can both get access to the state?
> 
> cheers,
> 
> Chris

Hi Chris, thanks for your input, I'm already following Eric's advice and I'm       
storing datemode in a previous step (users has the option to validate their        
excel file and while at it, I retrieve the data and store it), precluding the   
need for a deferred, which proved to be a really tough adversary.                                                          
I have even ended creating my own type to have a better error message for users and  
so far it seems to be working (actually I don't need the serialize method so I
didn't test it):

class XLSDate(object):
    """
    http://docs.pylonsproject.org/projects/colander/dev/extending.html
    """
    def serialize(self, node, appstruct):
        if appstruct is colander.null:
            return colander.null
        if not isinstance(appstruct, datetime.datetime):
            raise colander.Invalid(node, _('{0} is not a value that can be '
                 'parse into the excel internal date representation'.\
                         format(appstruct)))
        return appstruct and 'true' or 'false'

    def deserialize(self, node, cstruct):
        if cstruct is colander.null or cstruct==u'':
            return colander.null
        try:
            return float(cstruct)
        except ValueError, e:
            raise(colander.Invalid(node, _('{0} is not value that can be '
                'parse into a valid Excel date'.format(cstruct))))
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