[Python-ideas] PEP 428 - object-oriented filesystem paths

[Massimo DiPierro]

http://en.wikipedia.org/wiki/List_of_mathematical_symbols#Symbols

The + symbol means addition and union of disjoint sets. A path (including a fs path) is a set of links (for a fs path, a link is a folder name). Using the + symbols has a natural interpretation as concatenation of subpaths (sets) to for form a longer path (superset).

The / symbol means the quotient of a group. It always returns a subgroup. When I see path1 / path2 I would expect it to return all paths that start by path2 or contain path2, not concatenation.

The fact that string paths in Unix use the / to represent concatenation is accidental. That's just how the path is serialized into a string. In fact Windows uses a different separator. I do think a serialized representation of an object makes a good example for its abstract representation.

Massimo

On Oct 8, 2012, at 11:06 AM, Andrew McNabb wrote:

> On Tue, Oct 09, 2012 at 12:03:55AM +1100, Steven D'Aprano wrote:
>> / is a symbol that means whatever the class
>> gives it. It isn't like __init__ or __call__ that have defined
>> language semantics, and there is no rule that says that / means
>> division. I'll grant you that it's a strong convention, but it is
>> just a convention.
> 
> I'll grant you that the semantics of the __truediv__ method are defined
> by convention.
> 
>> But it's just a name. __add__ doesn't necessarily perform addition,
>> __sub__ doesn't necessarily perform subtraction, and __or__ doesn't
>> necessarily have anything to do with either bitwise or boolean OR.
>> Why should we insist that __*div__ (true, floor or just plain div)
>> must only be used for numeric division when we don't privilege other
>> numeric operators like that?
> 
> __add__ for strings doesn't mean numerical addition, but people find it
> perfectly natural to speak of "adding two strings," for example.  Seeing
> `string1.__add__(string2)` is readable, as is `operator.add(string1,
> string2)`.  Every other example of operator overloading that I find
> tasteful is analogous enough to the numerical operators to retain use
> the name.
> 
> Since this really is a matter of personal taste, I'll end my
> participation in this discussion by voicing support for Nick Coghlan's
> suggestion of a `join` method, whether it's named `join` or `append` or
> something else.
> 
> --
> Andrew McNabb
> http://www.mcnabbs.org/andrew/
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