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: Wed, 9 Nov 2011 19:09:38 -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 09.11.11 13:56, Eric Rasmussen wrote:
> Hi Mariano,
> 
> I was hoping one of the colander experts might jump in, but I'll go
> out on a limb and say there's probably not a really clean way to do
> exactly what you want. However, you might consider passing in a
> deferred missing function to the SchemaNode. It does bypass
> validation, but otherwise appears to do what you want. Here's an
> example (needs some cleanup):
> 
> import colander, datetime
> from xlrd import xldate_as_tuple
> 
> # missing values not validated!
> @colander.deferred
> def xldate_missing(node, kw):
>    book = kw.get('book')
>    datemode = getattr(book, 'datemode')
>    datefloat = kw.get('datefloat')
>    tupledate = xldate_as_tuple(datefloat, datemode)
>    return datetime.datetime(*tupledate)
> 
> class CUser(colander.MappingSchema):
>    id = colander.SchemaNode(colander.String())
>    xldate = colander.SchemaNode(colander.Date(), missing=xldate_missing)
> 
> if __name__ == '__main__':
>    """ assign floating date to bound keyword datefloat
>    deferred missing method will fill in value"""
>    cstruct = {'id':u'TEST'}
>    schema = CUser().bind(
>       book=type('Book', (object,), {'datemode':0}),
>       datefloat=40808.0)
>    schema.deserialize(cstruct)
>    print 'final xldate value: %s' % schema.children[1].deserialize()
> 
> Or if you have a default datemode that's used most of the time, you
> could use a preparer function that converts with the default, and then
> modify the value if needed with an after_bind callback.
> 
> Best,
> Eric
> 

Eric, thanks a lot for your time and detailed suggestion. I will try to apply
it right away and see how it works and let you know.

Regards,
Mariano

> 
> On Tue, Nov 8, 2011 at 9:16 AM, Eric Rasmussen <ericrasmus...@gmail.com> wrote:
> > Hi Mariano,
> >
> > I understand the issue now and see what you're trying to do. My initial
> > thought is this isn't possible with preparer because it takes a value as its
> > only argument and returns the value as-is or modified.
> >
> > However, I'll take a look at this again tonight if no one else knows a
> > solution off-hand.
> >
> > Best,
> > Eric
> >
> >
> >
> > On Tue, Nov 8, 2011 at 4:52 AM, Mariano Mara <mariano.m...@gmail.com> wrote:
> >>
> >> On 07.11.11 21:17, Eric Rasmussen wrote:
> >> > ï¿½ ï¿½Hi Mariano,
> >> > ï¿½ ï¿½I haven't had any trouble with this but it would help to see your
> >> > code
> >> > ï¿½ ï¿½to make sure I understand you correctly. The kw parameter should be
> >> > the
> >> > ï¿½ ï¿½second argument to your deferred widget, and it will let you access
> >> > ï¿½ ï¿½keyword arguments passed to the bind function like this:
> >> > ï¿½ ï¿½# deferred select widget
> >> > ï¿½ ï¿½@colander.deferred
> >> > ï¿½ ï¿½def deferred_widget(node, kw):
> >> > ï¿½ ï¿½ ï¿½ ï¿½options = kw.get('mykeyword', [])
> >> > ï¿½ ï¿½ ï¿½ ï¿½return widget.SelectWidget(values=options)
> >> > ï¿½ ï¿½# binding
> >> > ï¿½ ï¿½SomeSchema().bind(mykeyword=data)
> >> > ï¿½ ï¿½There's a more complete example at
> >> >
> >> > ï¿½[1]http://docs.pylonsproject.org/projects/colander/dev/binding.html?hig
> >> > ï¿½ ï¿½hlight=deferred, but let me know if I misunderstood.
> >> > ï¿½ ï¿½Thanks,
> >> > ï¿½ ï¿½Eric
> >> >
> >>
> >> Hi Eric, thanks a lot for your quick answer.
> >>
> >> In order to give a little of extra context regarding my problem: I'm using
> >> colander to
> >> deserialize an excel file. One of the values is a date and excel stores it
> >> as
> >> a float. The xlrd package provides a suitable method to turn that float
> >> into a
> >> proper date value, however it requires a 'datemode' parameter that can
> >> only be
> >> obtained once you opened and parsed the excel file. That's why I'm
> >> deferring
> >> this preparer.
> >>
> >> I managed to create the following auto contained example (this can be
> >> reproduced installing the xlrd package). After some rounds of debugging my
> >> understanding is that a deferred preparer method is unable to receive the
> >> kw
> >> parameter.
> >>
> >> import colander, datetime
> >> from xlrd import xldate_as_tuple
> >>
> >> @colander.deferred
> >> def deferred_xls_date(value, kw):
> >> ï¿½ ï¿½"""Preparer method to turn an excel float into the corresponding date
> >> ï¿½ ï¿½value. We will know the datemode parameter once the excel book has been
> >> ï¿½ ï¿½opened and parsed"""
> >> ï¿½ ï¿½if value is None or value=='': return None
> >> ï¿½ ï¿½datemode = getattr(kw.get('book'), 'datemode')
> >> ï¿½ ï¿½return xldate_as_tuple(value, datemode)
> >>
> >> class CUser(colander.MappingSchema):
> >> ï¿½ ï¿½id = colander.SchemaNode(colander.String())
> >>
> >> cstruct = {'id':u'TEST', 'sdate':40808.0}
> >> schema = CUser().bind(book=type('Book', (object,), {'datemode':0}))
> >> schema.add(colander.SchemaNode(colander.Date(),
> >> ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½preparer=deferred_xls_date,
> >> ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½validator=colander.Range(max=datetime.datetime.now())
> >> ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½))
> >> schema.deserialize(cstruct)
> >>
> >> This happens when you execute it:
> >>
> >> $ python colander_example.py
> >> Traceback (most recent call last):
> >> ï¿½File "colander_example.py", line 22, in <module>
> >> ï¿½ ï¿½schema.deserialize(cstruct)
> >> ï¿½File
> >> "/home/mariano/Code/SmD/env/lib/python2.7/site-packages/colander/__init__.py",
> >> line 1576, in deserialize
> >> ï¿½ ï¿½appstruct = self.typ.deserialize(self, cstruct)
> >> ï¿½File
> >> "/home/mariano/Code/SmD/env/lib/python2.7/site-packages/colander/__init__.py",
> >> line 477, in deserialize
> >> ï¿½ ï¿½return self._impl(node, cstruct, callback)
> >> ï¿½File
> >> "/home/mariano/Code/SmD/env/lib/python2.7/site-packages/colander/__init__.py",
> >> line 439, in _impl
> >> ï¿½ ï¿½result[name] = callback(subnode, subval)
> >> ï¿½File
> >> "/home/mariano/Code/SmD/env/lib/python2.7/site-packages/colander/__init__.py",
> >> line 475, in callback
> >> ï¿½ ï¿½return subnode.deserialize(subcstruct)
> >> ï¿½File
> >> "/home/mariano/Code/SmD/env/lib/python2.7/site-packages/colander/__init__.py",
> >> line 1579, in deserialize
> >> ï¿½ ï¿½appstruct = self.preparer(appstruct)
> >> TypeError: __call__() takes exactly 3 arguments (2 given)
> >>
> >>
> >>
> >> > ï¿½ ï¿½On Mon, Nov 7, 2011 at 8:43 PM, Mariano Mara
> >> > ï¿½ ï¿½<[2]mariano.m...@gmail.com> wrote:
> >> >
> >> > ï¿½ ï¿½ ï¿½Hi there, I have a deferred preparer I want to apply in schema
> >> > ï¿½ ï¿½ ï¿½binding,
> >> > ï¿½ ï¿½ ï¿½however it seems it's ignoring the kw parameter. Is this the
> >> > ï¿½ ï¿½ ï¿½expected behaviour
> >> > ï¿½ ï¿½ ï¿½or I'm missing some detail?
> >> > ï¿½ ï¿½ ï¿½TIA,
> >> > ï¿½ ï¿½ ï¿½Mariano
> >>
> >> --
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> >>
> >
> >
> 
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