[Python-Dev] Declaring setters with getters

[Guido van Rossum]

On 10/31/07, skip at pobox.com <skip at pobox.com> wrote:
>
>     Guido> I've come up with a relatively unobtrusive pattern for defining
>     Guido> setters. Given the following definition:
>
>     ...
>
> I'm a pretty naive user of properties, so can you explain to me how what you
> propose is better than
>
>     class C(object):
>         def __init__(self):
>             self._encoding = None
>
>         def get_encoding(self):
>             return self._encoding
>
>         def set_encoding(self, value):
>             if value is not None:
>                 unicode("0", value)  # Test it
>             self._encoding = value
>         encoding = property(get_encoding, set_encoding)
>
> ?

Mostly so it's easy to add a setter to a property that originally had
only a getter. For read-only properties, using

  @property
  def name(self):
      return <whatever>

is preferred over

  def get_name(self):
      return <whatever>
  name = property(get_name)

>     Guido> I'd also like to change property so that the doc string defaults
>     Guido> to the doc string of the getter.
>
> How about defaulting it to the first argument to property() which has a doc
> string?

I considered that briefly, but decided against it -- it could lead to
odd results if the getter has no docstring and the setter's docstring
is about setting only.

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