Question

I’m trying to match rc-update -s output in python.

m = re.match(r"^\s*(\w+)\s*\|{\s*(\w+)\s*}*$", " network | level1 level2 leveln ")

but m is always None

the hard part for me is getting the regex to match the n levels. I thought that using {}* would match the n levels, but as soon as I add the {} nothing matches.

thanks.

Answer 1

The curly braces (“{}”) do not do what you think they do, at least in this example.

You seem to want a non-matching group. With Python’s re, the syntax for this is (?:\s*(\w+)\s*), to match your example.

With this change to your example, I get:

>>> m = re.match(r"^\s*(\w+)\s*\|(?:\s*(\w+)\s*)*$", " network | level1 level2 leveln ")
>>> m
<_sre.SRE_Match object at 0x00F217B8>
>>> m.groups()
('network', 'leveln')

Note that the result only contains the last match for the repeated group. If you want to get all of the matches, match the entire expression containing the repetitions, and then parse that to find each of the matches. For example:

>>> m = re.match(r"^\s*(\w+)\s*\|((?:\s*\w+\s*)*)$", " network | level1 level2 leveln ")
>>> m.groups()
('network', ' level1 level2 leveln ')
>>> m.groups()[1].strip().split()
['level1', 'level2', 'leveln']

On a side note, this looks like something that would be much simpler to parse without regexps. As you can see, regexps have a lot of gotchas and become confusing very quickly.