How do I make Python's negative lookbehind less greedy?

Question

I've read all related posts and scoured the internet but this is really beating me.

I have some text containing a date.
I would like to capture the date, but not if it's preceded by a certain phrase.

A straightforward solution is to add a negative lookbehind to my RegEx.

Here are some examples (using findall).
I only want to capture the date if it isn't preceded by the phrase "as of".

19-2-11
something something 15-4-11
such and such as of 29-5-11

Here is my regular expression:

(?<!as of )(\d{1,2}-\d{1,2}-\d{2})

Expected results:

['19-2-11']
['15-4-11']
[]

Actual results:

['19-2-11']
['15-4-11']
['9-5-11']

Notice that's 9 not 29. If I change \d{1,2} to something solid like \d{2} on the first pattern:

bad regex for testing: (?<!as of )(\d{2}-\d{1,2}-\d{2})

Then I get my expected results. Of course this is no good because I'd like to match 2-digit days as well as single-digit days.

Apparently my negative lookbehind is quity greedy -- moreso than my date capture, so it's stealing a digit from it and failing. I've tried every means of correcting the greed I can think of, but I just don't know to fix this.

I'd like my date capture to match with the utmost greed, and then my negative lookbehind be applied. Is this possible? My problem seemed like a good use of negative lookbehinds and not overly complicated. I'm sure I could accomplish it another way if I must but I'd like to learn how to do this.

How do I make Python's negative lookbehind less greedy?

Answer 1

This has nothing to do with greediness. Greediness doesn't change whether a regular expression matches or not - it changes only the order in which the search is performed. The problem here is that your regular expression needs to be more specific to avoid unwanted matches.

To fix it you could require a word boundary just before your match:

(?<!as of )\b(\d{1,2}-\d{1,2}-\d{2})
#          ^^ add this