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[Python-Dev] file system path protocol PEP

Arthur Darcet arthur.darcet+list at m4x.org
Wed May 11 20:13:32 EDT 2016 
On 11 May 2016 at 22:51, Ethan Furman <ethan at stoneleaf.us> wrote:

> On 05/11/2016 01:44 PM, Serhiy Storchaka wrote:
>
> os.path
>>> '''''''
>>>
>>> The various path-manipulation functions of ``os.path`` [#os-path]_
>>> will be updated to accept path objects. For polymorphic functions that
>>> accept both bytes and strings, they will be updated to simply use
>>> code very much similar to
>>> ``path.__fspath__() if  hasattr(path, '__fspath__') else path``. This
>>> will allow for their pre-existing type-checking code to continue to
>>> function.
>>>
>>
>> I afraid that this will hit a performance. Some os.path functions are
>> used in tight loops, they are hard optimized, and adding support of path
>> protocol can have visible negative effect.
>>
>
> Do you have an example of os.path functions being used in a tight loop?
>

os.path.getmtime could be used in a tight loop, to sync directories with a
lot of files for instance.

% python3 -m timeit -s "import os.path; p = 'out'" "hasattr(p,
'__fspath__'), os.path.getmtime(p)"
100000 loops, best of 3: 2.67 usec per loop
% python3 -m timeit -s "import os.path; p = 'out'" "isinstance(p, (str,
bytes)), os.path.getmtime(p)"
100000 loops, best of 3: 2.45 usec per loop
% python3 -m timeit -s "import os.path; p = 'out'" "os.path.getmtime(p)"
100000 loops, best of 3: 2.02 usec per loop

a 25% markup is a lot imo.

a isinstance check prior to the hasattr might be a way to mitigate this a
bit (but it doesn't help much)
Granted, this example could be optimised by calling os.stat directly, which
is not in os.path, but still, worth considering
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