Greedy v/s Non-Greedy matching dilemma with python regex

Asked Jan 28 '20 at 21:38

Active Jan 28 '20 at 21:39

Viewed 13 times

As far as I read, ? is supposed to be the operator to indicate non-greedy(i.e. smallest first) matching in python regex. I am having trouble in relating matching for the following two similar regex strings:

Case 1:

>>> regex = re.compile(r'(Super|Bat|Spider|Ant){1,2}')
>>> regex.search('AntAnt-Man').group()
'AntAnt'
>>> regex = re.compile(r'(Super|Bat|Spider|Ant){1,2}?')
>>> regex.search('AntAnt-Man').group()
'Ant'

Case 2:

>>> regex.search('AntAnt-Man').group()
'AntAnt-Man'
>>> regex = re.compile(r'(Super|Bat|Spider|Ant){1,2}?-(Man)')
>>> regex.search('AntAnt-Man').group()
'AntAnt-Man'

Dilemma: If in case1, group method picks 'Ant' if using ?, why isn't the same happening for case2?

edited Jan 28 '20 at 21:39

eyllanesc

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asked Jan 28 '20 at 21:38

Tarun

Because matching starts at the leftmost location. Matches are searched for from left to right. – Wiktor Stribiżew Jan 28 '20 at 21:40
In case 2 your pattern which includes -Man must match AntAnt-Man because a shorter match isn’t possible once the first Ant is matched. Matching against FredAnt-Man would return Ant-Man. – DisappointedByUnaccountableMod Jan 28 '20 at 21:50

Greedy v/s Non-Greedy matching dilemma with python regex

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