Can I make these getters/setters?

Bruno Desthuilliers bruno.42.desthuilliers at websiteburo.invalid
Wed Sep 30 10:06:38 CEST 2009


Michael George Lerner a écrit :
> Hi,
> 
> As part of my GUI, I have lots of fields that people can fill in,
> defined like this:
> 
>         self.selection =  Pmw.EntryField(group.interior(),
>                                         labelpos='w',
>                                         label_text='Selection to use:
> ',
>                                         value='(polymer)',
>                                         )
> 
> I then use self.selection.get_value() and self.selection.set_value(),
> and those two functions are the only ways in which I care about
> self.selection. I've never really used properties, getters or setters
> before. I tried this, but it didn't work:
> 
> def __init__(self):
>         self._selection =  Pmw.EntryField(group.interior(),
>                                         labelpos='w',
>                                         label_text='Selection to use:
> ',
>                                         value='(polymer)',
>                                         )
>         self.selection = property(self._selection.get_value
> (),self._selection.set_value())

What you're passing here are the results of the calls to .get_value and 
.set_value, not the methods themselves. You'd want:

         self.selection = property(
            self._selection.get_value,
            self._selection.set_value
            )

But as Steven already mentioned, property only works as a class 
attribute, not as an instance attribute. What you need here is:

class Parrot(object):
   def __init__(self):
      self._selection =  Pmw.EntryField(...) 


   selection = property(
       lambda self: self._selection.get_value(),
       lambda self, value: self._selection.set_value(value)
       )


> Of course, I really have ~40 things that I'd like to do this for, not
> just one, so I'd like to find a fairly concise syntax.


the property object is just one possible application of the descriptor 
protocol. You could write your own custom descriptor (warning: untested 
code, may contains typos etc):

class FieldProperty(object):
     def __init__(self, fieldname):
         self._fieldname = fieldname

     def __get__(self, instance, cls):
         if instance is None:
            # can't work on the class itself
            return self
         return getattr(instance, self._fieldname).get_value()

     def __set__(self, instance, value):
         getattr(instance, self._fieldname).set_value(value)


class Parrot(object):
   def __init__(self):
      self._selection =  Pmw.EntryField(...) 


   selection = FieldProperty("_selection")



HTH



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