[Zope3-dev] Notations for paths (was comments on Guido's diary)

[Jim Fulton]

Steve Alexander wrote:
> 
>> I don't like this for two reasons:
>>
>> - It adds yet another way to do it, which is unpythonic. :)
> 
> 
> I explained my view of the difference between a location and a path in 
> another message. In my view, a location is always absolute.

I just responded. Locations are expressed as paths. The interoretation of
a path should be consistent regardless of what it''s used for.

>> - It should be possible to convert between the string and sequence forms
>>   with the simple expressions:
>>
>>   stringpath = '/'.join(tuplepath)
>>
>>   tuplepath = stringpath.split('/')
> 
> 
> This is not possible in general. I've had to correct code that tries to 
> convert between string locations and tuple locations using the simple 
> expressions above. They do not work for the root '/' or ('',). Relying 
> on the simple expressions caused a number of subtle and hard to track 
> down bugs that I fixed a couple of weeks ago.

That's surprizing, because Iv't found this mechanism to be quite robost in
the past.


>  >>> root_string = '/'
>  >>> root_tuple = ('',)
>  >>>
>  >>> '/'.join(root_tuple)
> ''
>  >>> root_string.split('/')
> ['', '']
>  >>> tuple(root_string.split('/'))
> ('', '')

This is interesting. Zope 2 treats trailing slashes as optional.

Still, I'm surprised that this hasn't been more of a problem in Zope 2.


> 
> I would recommend that, for correctness, code always uses the 
> convenience functions in Zope.App.Traversing.

Yes.

> We could also debate whether to redefine the definition of a location so 
> that it doesn't have this irregularity at the root.
> 
> Absolute paths and simple relative names (one step relative paths) are 
> used in Zope far more than relative paths. If we're always clear when 
> we're dealing with absolute paths, we don't need the '/' or ('',) at the 
> start, so we can use the simple expressions above.

For strings, a leading '/' must be required to indicate an absolute path.
Departing from this would be just to dang weird.

Maybe we should make string paths the only standard path notation.

Jim

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