Support for lazy quantifiers

[michaelmior]

Greenery doesn't seem to support lazy quantifiers, for example o{0,1}?. Currently I run into a parser error.

>>> greenery.parse('o{0,1}?')
/usr/lib/python3/dist-packages/requests/__init__.py:89: RequestsDependencyWarning: urllib3 (2.2.1) or chardet (3.0.4) doesn't match a supported version!
  warnings.warn("urllib3 ({}) or chardet ({}) doesn't match a supported "
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/mmior/.local/lib/python3.8/site-packages/greenery/parse.py", line 371, in parse
    raise NoMatch(f"Could not parse {string!r} beyond index {i}")
greenery.parse.NoMatch: Could not parse 'o{0,1}?' beyond index 6

[qntm]

Yes, this is deliberate. A regular expression is a concise description of a regular language, which is a set of strings, and greenery provides tools for manipulating those expressions. However, lazy quantifiers do not alter the regular language. The set of strings matched by /o{0,1}?/ is identical to the set of strings matched by /o{0,1}/ - they describe the same regular language. Lazy quantifiers do affect substring matches, but greenery does not actually provide matching functionality, that isn't what it's for.

[michaelmior]

@qntm Got it, thanks for the response. I guess that means it doesn't support lazy/greedy modifiers at all, which makes sense. Although I will say that it would be very helpful for my use case if the parser would accept such regexes anyway. I'm dealing with a scenario where I'd like to be able to handle as broad a set of expressions as possible.

While of course I could find a way to parse the expression using some other method and remove lazy and greedy modifiers before feeding to greenery, it would be nice to be able to skip this step.

[qntm]

There is a small amount of precedent for allowing syntax in the parser even though it doesn't make a material difference. I will consider this.

[michaelmior]

@qntm Thanks! I appreciate it :)

[michaelmior]

Also, I apologize that I missed that lack of support for lazy modifiers is explicitly mentioned in the README…

[qntm]

Give greenery-4.2.1 a try.

[michaelmior]

@qntm Works great! Thanks :)