PEP 8: on member variables vs. attributes

[Dan Bishop]

jbperez808 at yahoo.com (Jonathan P.) wrote in message news:<f57664b9.0301170041.46cc103e at posting.google.com>...
> From PEP 8:
> 
> Designing for inheritance
> 
>       ...  In general, never make data
>       variables public unless you're implementing essentially a
>       record.  It's almost always preferrable to give a functional
>       interface to your class instead (and some Python 2.2
>       developments will make this much nicer)...
> 
> But don't properties and data variables (as attributes) look 
> the same anyway?  So what's the diff between them, functionally
> speaking?

>>> class Foo(object):
...    def __init__(self):
...       self.__bar = ""
...    def __getBar(self):
...       return self.__bar
...    def __setBar(self, value):
...       if isinstance(value, str):
...          self.__bar = value
...       else:
...          raise TypeError("bar must be a string")
...    bar = property(__getBar, __setBar)
...
>>> baz = Foo()
>>> baz.bar = 4
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "<stdin>", line 10, in __setBar
TypeError: bar must be a string

If bar was just a data variable, you'd have no control over what got assigned to it.