Sorry, I should have tried harder. I see that the text
of the match is simply not consumed, so that:
m = re.search('(?=foo)fo', 'food')
succeeds, while
m = re.search('(?=fox)fo', 'food')
does not.
tobiah wrote:
> (?=...)
> Positive lookahead assertion. This succeeds if the contained regular
> expression, represented here by ..., successfully matches at the current
> location, and fails otherwise. But, once the contained expression has
> been tried, the matching engine doesn't advance at all; the rest of the
> pattern is tried right where the assertion started.
>
> I am unable to wrap my mind around this sentence. Could
> someone give me an example of how this works, and why
> it would be useful?
>
> Thanks,
>
> Toby
>
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