On 2022-08-17 08:25, Serhiy Storchaka wrote:
16.08.22 23:24, MRAB пише:
Other regex implementations have escape sequences for horizontal
whitespace (`\h` and `\H`) and vertical whitespace (`\v` and `\V`).
The regex module already supports `\h`, but I can't use `\v` because it
represents `\0x0b', as it does in the re module.
Now that someone has asked for it, I'm trying to find a nice way of
adding it, and I'm currently thinking that maybe I could use `\y` and
`\Y` instead as they look a little like `\v` and `\V`, and, also,
vertical whitespace is sort-of in the y-direction.
As far as I can tell, only ProgressSQL uses them, and, even then, it's
for what everyone else writes as `\b` and `\B`.
I want the regex module to remain compatible with the re module, in case
they get added there sometime in the future.
Opinions?
I do not like introducing escapes which are not supported in other RE
implementations. There is a chance of future conflicts.
Java broke compatibility in Java 8 by redefining \v from a single
vertical tab character to the vertical whitespace class. I am not sure
that it is a good example that we should follow, because different
semantic of \v in raw and non-raw strings is a potential source of bugs.
But with special flag which controls the meaning of \v it may be more safe.
Horizontal whitespace can be matched by [
\t\xA0\u1680\u180e\u2000-\u200a\u202f\u205f\u3000] in re or [\t\p{Zs}]
in regex. Vertical whitespace can be matched by
[\n\x0b\f\r\x85\u2028\u2029]. Note that there is a dedicated Unicode
category for horizontal whitespaces (excluding the tab itself), but not
for vertical whitespaces, it means that vertical whitespaces are less
important.
In any case it is simple to introduce special Unicode categories and use
\p{ht} and \p{vt} for horizontal and vertical whitespaces.
It's not just Java. Perl supports all 4 of \h, \H, \v and \V. That might
be why Java 8 changed.
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