On 9/17/2012 6:12 PM, Chris Angelico wrote:
On Tue, Sep 18, 2012 at 7:55 AM, Fernando Jiménez <the.me...@gmail.com> wrote:
Hi guys!
I'm noob in python and I would know how to correctly use the property. I
have read some things about it but I do not quite understand.
But I think it's a bad habit to use _ to change the visibility of the
attributes as in JAVA.
How to correctly use the property?
The single leading underscore is nothing to do with visibility; it's a
courteous request that external referents not touch something. In a
"consenting adults" model, that's usually sufficient.
For the most part, in fact, you don't need @property at all. Just make
an object's members public and save yourself the trouble! Unlike the
recommendation in C++ and Java, Python doesn't ask you to hide things
and write code to make them available. Instead of starting with
getters and setters, just start with a flat property, and move to
getters/setters only when you find you need them.
More examples:
A class has a data attribute that really is a simple attribute, no
property. You define a subclass that needs a calculation for the
attribute. So you use property in the subclass.
A class has an attribute that is a constant that must be computed. You
do not want to compute is unless and until needed.
def get_x(self):
try:
return self._x
except AttributeError:
self._x = calculate_x()
return self._
For a read-only attribute, don't provide a setter. If you do not like
"AttributeError: can't set attribute", provide one with a customized error.
But I think most of the data attributes in stdlib classes are straight
attributes.
--
Terry Jan Reedy
--
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