expose re._parse.parse_template publicly

[asottile]

Feature or enhancement

I would like to access parse_template to be able to eagerly validate that a regex replacement template is valid.

I'm using this in my python-based text editor to do find and replace. Currently I am reaching into sre_parse to get parse_template (which used to be a public-named module but was deprecated in 3.11)

I suspect this could be as simple as exposing parse_template -- my code doesn't actually care about the return value, simply whether it raises an exception or not

[sobolevn]

Refs #105456

[AlexWaygood]

Cc. @serhiy-storchaka

[raghunandanbhat]

I started working on this and added parse_template() in re.__init__.py

def parse_template(source, pattern):
    return _parse.parse_template(source, pattern)

Considering the very limited amount of documentation about this function, I would appreciate some help in testing it thoroughly and writing detailed documentation.

[serhiy-storchaka]

Is regex replacement template validation only what you need? Or do you need more information from the result?

Over a year ago, I wrote an implementation to compile a regex replacement template. I expected that this could be used to speed up critical code, like re.compile(), but I didn't see much difference compared to implicitly caching the compiled regex replacement templates. So I excluded it from #91524.

[asottile]

personally I only care about validation

[raghunandanbhat]

Since the parse_template() raises an error when replacement template is invalid, we could just use parse_template() as it is by exposing it publicly.

I think it is redundant to implement a function just to check if a replacement template is valid, instead we could use the existing one as it is.