python - Zero or one quantifier (`?`) does not seem to be greedy -


given these 2 test strings:

'eitherxory.' 'justy.'

i match 'x' (or nothing, if 'x' not present) , 'y', respectively:

('x', 'y') (none, 'y')

the pattern i've come (x)?.*?(y) matches are:

(none, 'y') (none, 'y')

what doing wrong?

i'm using python (import re; re.search(pattern, line).groups()) question generic.

one option use:

(?:(x).*)?(y)

we want match .* if have found x, can group them , move optional quantifier outside. avoids case when .* eats characters start of string.

keep in mind won't work if x occurs after y in string. use this:

(?=.*(x)).*(y)

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