Use `cached_property` for pathlib.Path instead of cache data in `property`

[Zheaoli]

Feature or enhancement

Proposal:

We can use

    @cached_property
    def _str_normcase(self):
        # String with normalized case, for hashing and equality checks
        if self.parser is posixpath:
            return str(self)
        else:
            return str(self).lower()

instead of

    @property
    def _str_normcase(self):
        # String with normalized case, for hashing and equality checks
        try:
            return self._str_normcase_cached
        except AttributeError:
            if self.parser is posixpath:
                self._str_normcase_cached = str(self)
            else:
                self._str_normcase_cached = str(self).lower()
            return self._str_normcase_cached

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

[picnixz]

This is tricky because:

• this could break downstream code
• this makes the attribute writable.
• this requires a __dict__ and the latter will be larger; IOW, __slots__ will need to include that __dict__.

I don't think this is worth the change. We can have a local decorator though that can ease our life for that.

[Zheaoli]

• this could break downstream code

I'm not getting this point. Would you mind tell me more detail about this?

[picnixz]

Oh, my bad, it's a private property, so it wouldn't be possible to break it. However the other points still stand (especially the last one; we do not want to add a __dict__ to path objects).

[cmaloney]

cc: @barneygale (pathlib code owner)

[barneygale]

Adding __dict__ is a bit of a deal-breaker I'm afraid :( but thanks for giving it some thought all the same. There might be time to save by replacing the try: ... except AttributeError: ... pattern with something else - please do log another issue if you find a way to make it faster without adding __dict__ :)