The Python standard library and PEP8

Emmanuel Surleau emmanuel.surleau at
Mon Apr 20 08:05:01 CEST 2009

On Monday 20 April 2009 01:48:04 Steven D'Aprano wrote:

> The problem is, I believe, that people wrongly imagine that there is One
> True Way of a language being "object-oriented", and worse, that the OTW
> is the way Java does it. (If it were Smalltalk, they'd at least be able
> to make the argument that Smalltalk invented the perfect OO language 
> every change since then was corruption.) This is of course nonsense, but
> many people fall for it. "The way I'm used to is the One True Way".
> As far as str.len versus len(str), apart from saving one character, I
> don't see any advantage to one over the other. It really depends on what
> you're used to.
> It also depends on whether you see the length of a data structure as a
> property of the data, or the result of an operation ("counting") on the
> data structure. We often fall into the trap of saying such things as "the
> string HAS A length of 42" when what we really mean is "if you count the
> elements of the string we find 42 of them". I don't believe that the
> relationship between strings and length is a has-a relationship. I
> believe it is a property requiring a function (counting) to emerge, and
> therefore under OO principles, length should *not* be an attribute and
> Java et al are guilty of misuse of OO in making length an attribute.

This didn't quite make sense. Methods are "abilities" an object has. Why 
shouldn't a string be able to compute its length?

> If you don't agree, consider an analogy: think about what it means to say
> that "Fred has a height", compared to "Fred has a left arm". You can
> point to Fred's left arm, you can surgically remove it, in principle at
> least you could surgically attach a left arm to somebody who didn't have
> one. The relationship between "Fred" and "left arm" is most certainly a
> "has-a" relationship. But the same isn't true for height: you can't
> surgically remove Fred's height, and you can't even point to the part of
> Fred that is his height. The length of a string is like height.

As noted above, nothing would stop Fred from having the ability to 
"computeHeight()", though. I guess you could say that what I find silly is that 
String objects have a number of abilities, which:
- are more complicated than retrieving their own length
- most likely use len() internally anyway

And yet, when asked, it's not able to do something as basic as tell its 
length. This seems inconsistent to me.



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