A regular expression question

[Cpcp Cp]

Look this

>>> import re
>>> text="asdfnbd]"
>>> m=re.sub("n*?","?",text)
>>> print m
?a?s?d?f?n?b?d?]?

I don't understand the 'non-greedy' pattern.

I think the repl argument should replaces every char in text and outputs "????????".