Converts markdown inline links to reference links. Inspired by Brett Terpstra's to reference service, written in Ruby. This can be used as an OS X service or in a Editorial workflow.

to_reference.py

#!/usr/bin/env python

import re
import operator
import re

RE_REF = "\\[(.+?)\\]:\\s*(\\S+(\\s+?\".*\")?)\\s*"
RE_LINK = "\\((https?://(.+?))\\)"


def replace_links(input_, done):
    def replace_links(match):
        url = match.group(1)

        if url not in (x['url'] for x in done):
            parts = match.group(2).split('.')
            name = parts[0] if len(parts) == 1 or len(parts) == 2 else parts[1]

            while name in (x['name'] for x in done):
                num = re.search("(.+?) ([0-9]+?)$", name)
                name = name + " 2" if not num else num.group(1) + " " + str(int(num.group(2)) + 1)

            done.append({'url': url, 'name': name})
        else:
            name = [x['name'] for x in done if x['url'] == url][0]

        return "[{}]".format(name)

    output_ = re.sub(RE_LINK, replace_links, input_)
    return output_, done


def replace_refs(input_, done):
    def replace_refs(match):
        name = match.group(1)
        url = match.group(2)

        done.append({'url': url, 'name': name})

        return None

    output_ = re.sub(RE_REF, replace_refs, input_)
    return output_, done


def start(input_):
    input_, done = replace_links(*replace_refs(input_, []))
    if len(done) > 0:
        return input_ + '\n' + '\n'.join(['[{}]: {}'.format(d['name'], d['url']) for d in done])
    else:
        return input_


try:
    import editor
    import workflow

    input_ = workflow.get_input()
    output_ = start(input_)
    workflow.set_output(output_)

except ImportError:
    import sys
    input_ = sys.stdin.read()
    output_ = start(input_)
    print output_