[Python-Dev] Declaring setters with getters (original) (raw)

Guido van Rossum guido at python.org
Sat Nov 10 07:03:03 CET 2007

D'oh. I forgot to point to the patch. It's here: http://bugs.python.org/issue1416

On Nov 9, 2007 10:00 PM, Guido van Rossum <guido at python.org> wrote:

To follow up, I now have a patch. It's pretty straightforward.

This implements the kind of syntax that I believe won over most folks in the end: @property def foo(self): ... @foo.setter def foo(self, value=None): ... There are also .getter and .deleter descriptors. This includes the hack that if you specify a setter but no deleter, the setter is called without a value argument when attempting to delete something. If the setter isn't ready for this, a TypeError will be raised, pretty much just as if no deleter was provided (just with a somewhat worse error message :-). I intend to check this into 2.6 and 3.0 unless there is a huge cry of dismay. Docs will be left to volunteers as always. --Guido

On Oct 31, 2007 9:08 AM, Guido van Rossum <guido at python.org> wrote: > I've come up with a relatively unobtrusive pattern for defining > setters. Given the following definition: > > def propset(prop): > assert isinstance(prop, property) > def helper(func): > return property(prop.get, func, func, prop.doc) > return helper > > we can declare getters and setters as follows: > > class C(object): > > encoding = None > > @property > def encoding(self): > return self.encoding > > @propset(encoding) > def encoding(self, value=None): > if value is not None: > unicode("0", value) # Test it > self.encoding = value > > c = C() > print(c.encoding) > c.encoding = "ascii" > print(c.encoding) > try: > c.encoding = "invalid" # Fails > except: > pass > print(c.encoding) > > I'd like to make this a standard built-in, in the hope the debate on > how to declare settable properties. > > I'd also like to change property so that the doc string defaults to > the doc string of the getter. > > -- > --Guido van Rossum (home page: http://www.python.org/~guido/) >

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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