python re.search quantifier

Question

I have this:-

re.search("^[47]{2:}$", '447447')

... and was expecting it to return True. But somehow it does not.

How come? My understanding is that it was suppose to match any number which has any combination of 4 or 7, with at least 2 digits. Is that correct?

Answer 1

It should probably be "^[47]{2,}$" .

I visit the regular expression syntax page quite often, because I find it hard to remember all of the little tricks for building regexes.

Answer 2

The syntax is {m,n} where n could be omitted.

Fix:

re.search("^[47]{2,}$", '447447')

See RegEx syntax: https://docs.python.org/3/library/re.html#regular-expression-syntax