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

Koos Zevenhoven k7hoven at gmail.com
Thu May 12 05:52:44 EDT 2016

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.

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