[Python-ideas] Better stdlib support for Path objects

[M.-A. Lemburg]

On 07.10.2014 11:48, Nick Coghlan wrote:
> On 7 Oct 2014 04:26, "Barry Warsaw" <barry at python.org> wrote:
>>
>> On Oct 06, 2014, at 11:04 AM, Guido van Rossum wrote:
>>
>>> You can construct a Path from an argument that can be either a string or
>>> another Path. Example:
>>>
>>>>>> from pathlib import Path
>>>>>> p = Path('/etc/passwd')
>>>>>> q = Path(p)
>>>>>> p == q
>>> True
>>>>>>
>>>
>>> So you could start refactoring stdlib code to use Path internally without
>>> forcing the callers to use Path, but still *allow* the callers to pass a
>>> Path. Though I'm not sure how this would work for return values without
>>> breaking backwards compatibility -- you'd have to keep returning strings
>>> and the callers would have to use the same mechanism to go back to using
>>> Paths.
>>
>> That's a very interesting perspective, and one I'd like to pursue further.
> 
> pathlib is quite high level, so there's a chance of introducing undesirable
> circular dependencies in introducing it too broadly.
> 
> With ipaddress and, as far as I am aware, pathlib, the intent was for it to
> be useful as a manipulation library, but to drop back to a serialised
> representation for transfer to other libraries (including the rest of the
> stdlib). This helps avoid the monolithic object model coupling that tends
> to pervade large Java applications.
> 
> If the current spelling of that is too verbose/awkward/error prone, then
> I'd prefer to see that tackled directly (e.g. by introducing some
> appropriate calculated properties), rather than switching to the highly
> coupled all pervasive standard library change we were trying to avoid.

The approach to use pathlib internally in the stdlib while making
sure that callers will get strings as return values should work fine.

We've been using a similar approach with mxURL in some of our application
server code. mxURL which provides a parsed URL object that implements
common tasks such as joining URLs, rebuilding, etc. The approach makes
code more readable, you get the option of passing in a string or an
already parsed URL object (saving some overhead) and code using the
APIs get strings which prevents other code from complaining about
a wrong type.

-- 
Marc-Andre Lemburg
eGenix.com

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