[Python-Dev] file system path protocol PEP

[Koos Zevenhoven]

On Thu, May 12, 2016 at 11:14 AM, Serhiy Storchaka <storchaka at gmail.com> wrote:
>
> This is cheap in C, but os.path functions are implemented in Python. They
> have to make at least one function call (os.fspath(), hasattr() or
> isinstance()), not counting a bytecode for retrieving arguments, resolving
> attributes, comparing, jumps. Currently os.path functions use tricks to
> avoid overheads
>

I suppose a C-implemented version of fspath *called from python* might
be the fastest option at least in some cases. After all, a function
call (isinstance or hasattr) is likely anyway, unless of course `try:
path.__fspath__` is used.

> Yet one problem is that currently many os,path functions work with
> duck-typed strings (e.g. UserString). Using os.fspath() likely limit
> supported types to str, bytes and types that support the path protocol.
>

Something like

path = path.__fspath__() if hasattr(path, '__fspath__') else path

as currently in the PEP, would not have this problem. However, I
wonder whether such duck string paths actually exist (although it does
remind me of my earlier experiments for solving the pathlib
compatibility problem ;-).


-- Koos

P.S: I think it's great that you are concerned about the performance,
and I find it important. However, this does feel like premature
optimization to me at this point. We should first decide what
functions should support the protocol, and after that, find the
performance concerns and fix them. I have the feeling that the cases
where this would be a performance bottleneck are quite rare, but if
they are not, they may well be fixable.