Re: [Zope3-dev] keeping attributes abstract
Sam Stainsby wrote: So I'm inclines to use the IFooB approach by default to achieve more abstract attributes. Am I missing something here in the IFooA approach that allows me to do this anyway? You are :) Python has properties. They give you a good migration path from a simple attribute to what you would otherwise have to use getter/setters for. An example would help. Today you do this: class Foo(Persistent): implements(IFooB) bar = None And then you decide, oops I need to calculate bar every time it's accessed. Then you can do this: class Foo(Persistent): implements(IFooB) @property def bar(self): return time.time() * 2 # crazy thing, but just an example But that bar is read-only, what if you also want to be able to set bar, you can do this: class Foo(Persistent): implements(IFooB) @apply def bar(self): doc = The bar attribute def fset(self, bar): if bar is None: self._bar = 47 else: self._bar = bar def fget(self): return self._bar * 44 return property(**locals) Some people like a more explicit version of the last line, if so you can use return property(fset, fget, None, doc). (WARNING: I didn't actually run any of the code in this message, typos may have crept in) -- Benji York Senior Software Engineer Zope Corporation ___ Zope3-dev mailing list Zope3-dev@zope.org Unsub: http://mail.zope.org/mailman/options/zope3-dev/archive%40mail-archive.com
Re: [Zope3-dev] keeping attributes abstract
On Wednesday 08 March 2006 23:52, Sam Stainsby wrote: No 'bar' attribute needed! I'll note that in the Python community we consider it an advantage of using attributes/properties versus accessor and mutator methods. This distinction between an attribute- versus method-centric object oriented programming language has been discussed in many articles. Note that we provide several other mechanisms to extend functionality; for example, the event system. Overall Zope (like most other Python code) is optimized to work with attributes/properties. We just like them too much! :-) Regards, Stephan -- Stephan Richter CBU Physics Chemistry (B.S.) / Tufts Physics (Ph.D. student) Web2k - Web Software Design, Development and Training ___ Zope3-dev mailing list Zope3-dev@zope.org Unsub: http://mail.zope.org/mailman/options/zope3-dev/archive%40mail-archive.com
Re: [Zope3-dev] keeping attributes abstract
On Thu, Mar 09, 2006 at 07:11:20AM -0500, Stephan Richter wrote: | On Wednesday 08 March 2006 23:52, Sam Stainsby wrote: | No 'bar' attribute needed! | | I'll note that in the Python community we consider it an advantage of using | attributes/properties versus accessor and mutator methods. This distinction | between an attribute- versus method-centric object oriented programming | language has been discussed in many articles. | | Note that we provide several other mechanisms to extend functionality; for | example, the event system. Overall Zope (like most other Python code) is | optimized to work with attributes/properties. We just like them too much! :-) Not to mention that you can still use accessors/mutators with plain attributes, and then store the actual value under a different name to avoid the clash: class FooX(Persistent): implements(IFooB) _bar = None def setBar(self, bar): doSomething() self._bar = bar def getBar(self): doSomethingElse() return self._bar bar = property(getBar, setBar) -- Sidnei da Silva Enfold Systems, Inc. http://enfoldsystems.com ___ Zope3-dev mailing list Zope3-dev@zope.org Unsub: http://mail.zope.org/mailman/options/zope3-dev/archive%40mail-archive.com
