How to properly iterate with re.sub() in Python

Question

I want to make a Python script that creates footnotes. The idea is to find all strings of the sort \"Some body text.{^}{Some footnote text.}\" and replace them with

Answer 1

It seems like a good fit for a closure:

def make_footnote_counter(start=1):
    count = [start - 1] # emulate nonlocal keyword
    def footnote_counter(match):
        count[0] += 1
        return "<sup>%d</sup>" % count[0]
    return footnote_counter

new_body_text = re.sub(pattern, make_footnote_counter(), text)

Answer 2

A variation and Python-3-only solution:

def make_create_footnote_numbers(start=1):
    count = start - 1
    def create_footnote_numbers(match):
        nonlocal count
        count += 1
        return "<sup>{}</sup>".format(count)
    return create_footnote_numbers

new_body_text = re.sub(pattern, make_create_footnote_numbers(), text)

Answer 3

Any callable can be used, so you could use a class to track the numbering:

class FootnoteNumbers(object):
    def __init__(self, start=1):
        self.count = start - 1

    def __call__(self, match):
        self.count += 1
        return "<sup>{}</sup>".format(self.count)


new_body_text = re.sub(pattern, FootnoteNumbers(), text)

Now the counter state is contained in the FootnoteNumbers() instance, and self.count will be set anew each time you start a re.sub() run.