Question

Given a string, how do I extract all sequences of exactly 4 digits?

That is, for 1234 12 12345 1bc5 9876 I want to get [1234, 9876].

I got as far as re.findall('\D\d\d\d\d\D'), but that fails on text boundaries (when there’s no character before/after a match).

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Solution preferably using Python 2.7, but I guess this is pretty general, any language will do.

Answer 1

The general answer is surprisingly complicated, see here for more info. However in this particular case, we can simply use a word-boundary assertion \b:

re.findall(r'\b\d{4}\b', ....)