@x.setter property implementation

Floris Bruynooghe floris.bruynooghe at gmail.com
Fri Apr 11 11:16:17 CEST 2008


On Apr 10, 5:09 pm, Arnaud Delobelle <arno... at googlemail.com> wrote:
> On Apr 10, 3:37 pm, Floris Bruynooghe <floris.bruynoo... at gmail.com>
> wrote:
>
>
>
> > On Apr 7, 2:19 pm, "Andrii V. Mishkovskyi" <misho... at gmail.com> wrote:
>
> > > 2008/4/7, Floris Bruynooghe <floris.bruynoo... at gmail.com>:
>
> > > >  Have been grepping all over the place and failed to find it.  I found
> > > >  the test module for them, but that doesn't get me very far...
>
> > > I think you should take a look at 'descrobject.c' file in 'Objects' directory.
>
> > Thanks, I found it!  So after some looking around here was my
> > implementation:
>
> > class myproperty(property):
> >     def setter(self, func):
> >         self.fset = func
>
> > But that doesn't work since fset is a read only attribute (and all of
> > this is implemented in C).
>
> > So I've settled with the (nearly) original proposal from Guido on
> > python-dev:
>
> > def propset(prop):
> >     assert isinstance(prop, property)
> >     @functools.wraps
> >     def helper(func):
> >         return property(prop.fget, func, prop.fdel, prop.__doc__)
> >     return helper
>
> > The downside of this is that upgrade from 2.5 to 2.6 will require code
> > changes, I was trying to minimise those to just removing an import
> > statement.
>
> > Regards
> > Floris
>
> Here's an implementation of prop.setter in pure python < 2.6, but
> using sys._getframe, and the only test performed is the one below :)
>
> import sys
>
> def find_key(mapping, searchval):
>     for key, val in mapping.iteritems():
>         if val == searchval:
>             return key
>
> _property = property
>
> class property(property):
>     def setter(self, fset):
>         cls_ns = sys._getframe(1).f_locals
>         propname = find_key(cls_ns, self)
>         # if not propname: there's a problem!
>         cls_ns[propname] = property(self.fget, fset,
>                                     self.fdel, self.__doc__)
>         return fset
>     # getter and deleter can be defined the same way!
>
> # -------- Example -------
>
> class Foo(object):
>     @property
>     def bar(self):
>         return self._bar
>     @bar.setter
>     def setbar(self, x):
>         self._bar = '<%s>' % x
>
> # -------- Interactive test -----
>
> >>> foo = Foo()
> >>> foo.bar = 3
> >>> foo.bar
> '<3>'
> >>> foo.bar = 'oeufs'
> >>> foo.bar
> '<oeufs>'
>
> Having fun'ly yours,

Neat!

Unfortunatly both this one and the one I posted before work when I try
them out on the commandline but both fail when I try to use them in a
module.  And I just can't figure out why.

Floris



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