[Python-Dev] PEP 8 updates/clarifications

[Phillip J. Eby]

At 09:59 AM 12/12/2005 -0600, skip at pobox.com wrote:

>     Jim> That's why, in my suggested writeup, I suggested that attributes
>     Jim> should be used if the accessors are trivial.
>
>In my experience it's difficult to find the locations where another module
>mucks with your object's state.  Using properties or accessor methods
>coupling between modules is reduced and you can be more confident that the
>only place an object's state is modified directly is in its own code.

So?

There is no reason for you to care about this in advance of actual 
requirements.  Normal instance variables should be used for normal instance 
variable things, until you have a need to do something when they 
change.  Then, and only then, is it appropriate to introduce 
properties.  Otherwise, you're just wasting your time with busywork and 
annoying the heck out of people trying to read your code.  Python is not 
Java, and Java's use of getters and setters is a reflection of its 
inadequacies as a programming language, not a badge of strength.  They're a 
bug, not a feature.

What *would* be a nice feature to add to Python would be a descriptor that 
stores the value of the property in the object dictionary, but calls a 
function whenever the attribute is changed.  So then you could do:

      @setter
      def somevar(self, value):
          # update attrs affected by changing self.somevar

This is the shortest upgrade path for the common case of an attribute's 
lifetime.  First, it's just a regular __dict__ attribute, and then you 
maybe want to do something when it changes, but you still want it readable 
and stored normally, without having to have two attribute names (one public 
and one private).