In a message of Fri, 26 Aug 2005 18:24:33 EDT, Arthur writes:
And am hoping he is quite wrong in the assessment that "information hiding" is a base requirement for information science. ;)
He is quite correct, but 'hiddenness' is not an infinite human good, such as health. It is quite possible to hide too much. Whether 'having things work like magic' is a good thing or not is always a tricky judgement call.
Kirby seems comfortable in the Meyerist camp.
But I feel my anti-Meyerist sentiments are somehow bound to my pro-Python sentiments. So am having trouble with my Meyerist Python friend's stance .
Art
My guess is that you think that properties violate 'Explicit is better than implicit.' In the example in http://www.python.org/2.2.3/descrintro.html#property where x is restricted to positive values.
a = C() a.x = 10 print a.x 10 a.x = -10 print a.x 0 # I think that Art thinks this is too much magic a.setx(12) print a.getx() 12
One nice thing about overwriting __getattr__ and __setattr__ is that when you are done you have something that fairly shrieks 'black magic here'. Properties look innocuous. Some people go quite nuts with them, and use them whenever possible, as if there was something wrong with simple assignment in the first place. Worst of all, they are easy enough to use that all the would-be-Nannies in the world can trivially write code to prevent you doing what they think is unwise. This is most irritating when you are wiser -- or more imaginative than they are. This bit us the other day. Somebody naively thought that not allowing certain variables to be set to zero would be a swell way to avoid divide by zero errors. The problem is that the natural idiom used all over the codebase is: x = fast-way-to-solve-the-equation-works-most-of-the-time(**argv) if x is 0: # too bad x = do-it-the-hard-and-slow-way(**argv) He stuck his property in, and all over campus people started getting weird mysterious errors. People who tried to debug it and suddenly found out that _assignment_ 'wasn't working' concluded that '_Python_ was broken'. Their mental model of 'how computer languages work' doesn't include properties. Laura
-----Original Message----- From: Laura Creighton [mailto:lac@strakt.com]
One nice thing about overwriting __getattr__ and __setattr__ is that when you are done you have something that fairly shrieks 'black magic here'. Properties look innocuous. Some people go quite nuts with them, and use them whenever possible, as if there was something wrong with simple assignment in the first place.
Yes. Yes. And in that way can be a bit of a trap to those of us feeling our way. A trap I find I fell into a bit. Which = in essence - is why I thought a discussion of the subject pertinent. I have disagreed with an aspect of Python design, which in IMO consciously obscures functions and concepts related to the copying of objects. Guido seems to feel strongly that too much visibility here encourages overuse by novices. Maybe true. But I think the lesson inherent in "copy" is worth the risk. IMO, the degree of visibility of properties is a clearer case of this kind of issue. Less upside to it. Art
-----Original Message----- From: Laura Creighton [mailto:lac@strakt.com]
My guess is that you think that properties violate 'Explicit is better than implicit.'
Not exactly. More like I think that it encourages "theory", and I appreciate Python as a-a-theoretical. The counter argument is that Python is so a-theoretical as to not be opposed to the imposition, with it, of any theoretical approach a practitioner might find appropriate or want to explore. And properties fit in there somewhere. Art
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Laura Creighton