GH-119518: Stop interning strings in pathlib

[barneygale]

Remove sys.intern(str(x)) calls when normalizing a path in pathlib. This speeds up str(Path('foo/bar')) by about 10%.

As mentioned in the issue, I've never been able to establish if/when string interning is useful in pathlib, nor that we're using it in the best way. It feels negligent to leave it in the code.

• Issue: Stop manually interning strings in pathlib #119518

[vstinner]

LGTM. I am not convinced that interning strings is a good idea according to issues listed in #119518.

[barneygale]

Thank you both!

[geertj]

Can this be back ported to 3.13? The interning causes memory usage to grow indefinitely on a free threaded build.

[vstinner]

Can this be back ported to 3.13? The interning causes memory usage to grow indefinitely on a free threaded build.

IMO it's too late to backport such change. cc @colesbury

[colesbury]

Maybe we could consider something like the following in 3.13:

if sysconfig.get_config_var("Py_GIL_DISABLED"):
    return drv, root, [x for x in rel.split(sep) if x and x != '.']

parsed = [sys.intern(str(x)) for x in rel.split(sep) if x and x != '.']
return drv, root, parsed

In other words, avoid interning in the free-threaded build, but don't change the behavior in the 3.13 default build.