PEP on path module for standard library

[George Sakkis]

"Andrew Dalke" <dalke at dalkescientific.com> wrote:

> [snipped]
>
> > Take for example the case where a PhoneNumber class is subclass
> > of int. According to LSP, it is perfectly ok to add phone numbers
> > together, subtract them, etc, but the result, even if it's a valid
> > phone number, just doesn't make sense.
>
> Mmm, I don't think an integer is a good model of a phone number.
> For example, in the US
>   00148762040828
> will ring a mobile number in Sweden while
>   148762040828
> will give a "this isn't a valid phone number" message.

That's why phone numbers would be a subset of integers, i.e. not every integer would correspond to a
valid number, but with the exception of numbers starting with zeros, all valid numbers would be an
integers. Regardless, this was not my point; the point was that adding two phone numbers or
subtracting them never makes sense semantically.

> [snipped]
>
> > I just noted that conceptually a path is a composite object consisting of
> > many properties (dirname, extension, etc.) and its string representation
> > is just one of them. Still, I'm not suggesting that a 'pure' solution is
> > better that a more practical that covers most usual cases.
>
> For some reason I think that
>
>   path.dirname()
>
> is better than
>
>   path.dirname
>
> Python has properties now so the implementation of the latter is
> trivial - put a @property on the line before the "def dirname(self):".

Sorry, I used the term 'property' in the broad sense, as the whole exposed API, not the specific
python feature; I've no strong preference between path.dirname and path.dirname().

> I think that the string representation of a path is so important that
> it *is* the path.

There are (at least) two frequently used path string representations, the absolute and the relative
to the working directory. Which one *is* the path ? Depending on the application, one of them woud
be more natural choice than the other.

> I trust my intuition on this, I just don't know how to justify it, or
> correct it if I'm wrong.

My intuition also happens to support subclassing string, but for practical reasons rather than
conceptual.

George