Find out number of capture groups in Python regular expressions
python, regex
Solution
def num_groups(regex):
return re.compile(regex).groups
Problem
Is there a way to determine how many capture groups there are in a given regular expression? I would like to be able to do the follwing: ``` def groups(regexp, s): """ Returns the first result of re.findall, or an empty default >>> groups(r'(\d)(\d)(\d)', '123') ('1', '2', '3') >>> groups(r'(\d)(\d)(\d)', 'abc') ('', '', '') """ import re m = re.search(regexp, s) if m: return m.groups() return ('',) * num_of_groups(regexp) ``` This allows me to do stuff like: ``` first, last, phone = groups(r'(\w+) (\w+) ([\d\-]+)', 'John Doe 555-3456') ``` However, I don't know how to implement `num_of_groups`. (Currently I just work around it.) EDIT: Following the advice from rslite, I replaced `re.findall` with `re.search`. `sre_parse` seems like the most robust and comprehensive solution, but requires tree traversal and appears to be a bit heavy. MizardX's regular expression seems to cover all bases, so I'm going to go with that.