Lookahead in Group

[Álvaro Paiva]

Lookahead assertion
(?=...)

from mre import Regex, Group

# Example of how it can work 1
print(Regex("Isaac", Group(" Asimov", lookahead=True)))

# Output: Isaac(?= Asimov)
# Regex without lookahead: Isaac( Asimov)

Negative lookahead assertion
(?!...)

from mre import Regex, Group

# Example of how it can work 1
print(Regex("Isaac", Group(" Asimov", lookahead=False)))

# Output: Isaac(?! Asimov)
# Regex without lookahead: Isaac( Asimov)

Note: the default value of the lookahead parameter is None.

[Samuel Gaist]

Hi,

I'd like to take on this one :-)

[Samuel Gaist]

I would say there's something wrong here in mixing Group with lookahead (and lookbehind for that mather). They are different things. Looking around in a regex is a non-capturing operation and has a different semantic than grouping although in uses the same symbol to start. I would recommend having a separated class for that.

[Álvaro Paiva]

@sgaist

I agree with you. I really didn’t try to do that. The classes could be created:

• LookaheadGroup (or just Lookahead);
• LookbehindGroup (or just Lookbehind).

Both could inherit from Group, passing non_capturing=False in the parent class's constructor.

#7