Operator Precedence/Boolean Logic

Rustom Mody rustompmody at gmail.com
Wed Jun 29 09:30:36 EDT 2016


On Wednesday, June 29, 2016 at 6:38:16 PM UTC+5:30, Steven D'Aprano wrote:
> On Wed, 29 Jun 2016 08:21 pm, Rustom Mody wrote:
> > 3. Regular Expressions which mathematically are related to automata
> >   And pragmatically are (more) present in python than the first two
> 
> Can you even have an empty regular expression? What does it match? Possibly
> nothing at all.
> 
> Ideally, I would have the empty regular expression be falsey, and all others
> truthy, but I wouldn't be too upset if all regexes were True.

Salutations!

Chris fell into the trap -- if I take his "" as
> I think that's about as empty as a regex can be, 

You have not fallen in... Admirable!
What you need is a negative lookahead empty re  (?!)


>>> re.findall("", "")
['']
>>> re.findall("(?!)", "")
[]
>>> re.findall("(?!)", "a")
[]
>>> re.findall("", "a")
['', '']
>>> 

The other answers -- graphs and automata -- are questionable and/or wrong

You may wish to think about them again?



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