[Python-Dev] file system path protocol PEP (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Sat May 14 08:24:04 EDT 2016

On 14 May 2016 at 19:36, Sven R. Kunze <srkunze at mail.de> wrote:

Fine example. Thinking naively, I would say, when somebody made an effort to write fspath, it should be respected. Maybe, that's just me.

Over time, we've generally moved towards treating subclasses as if they were the base class where protocols are concerned, and encouraging the use of composition if people don't actually want that "is-a" behaviour.

For example, compare the int protocol to the last major type protocol we added, index:

from operator import index class MyInt(int): ... def int(self): ... return 42 ... def index(self): ... return 42 ... x = MyInt(5) x 5 int(x) 42 index(x) 5

In the case of retroactively added protocols like operator.index() and os.fspath(), where inheritance from the relevant builtin type was previously the only option, retaining that behaviour is also the only way to avoid a performance regression for those subclasses.

Cheers, Nick.

-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia

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