How to extract markdown links with a regex?

user_16199908 0
Viewed 1082

I currently have the Python code for parsing markdown text in order to extract the content inside the square brackets of a markdown link along with the hyperlink.

import re

# Extract []() style links
link_name = "[^]]+"
link_url = "http[s]?://[^)]+"
markup_regex = f'\[({link_name})]\(\s*({link_url})\s*\)'

for match in re.findall(markup_regex, '[a link](https://www.wiki.com/atopic_(subtopic))'):
    name = match[0]
    url = match[1]
    print(url)
    # url will be https://wiki.com/atopic_(subtopic

This will fail to grab the proper link because it matches up to the first bracket, rather than the last one.

How can I make the regex respect up till the final bracket?

python-re python regex
2 Answers

For those types of urls, you'd need a recursive approach which only the newer regex module supports:

import regex as re

data = """
It's very easy to make some words **bold** and other words *italic* with Markdown. 
You can even [link to Google!](http://google.com)
[a link](https://www.wiki.com/atopic_(subtopic))
"""

pattern = re.compile(r'\[([^][]+)\](\(((?:[^()]+|(?2))+)\))')

for match in pattern.finditer(data):
    description, _, url = match.groups()
    print(f"{description}: {url}")

This yields

link to Google!: http://google.com
a link: https://www.wiki.com/atopic_(subtopic)

See a demo on regex101.com.

This cryptic little beauty boils down to

\[([^][]+)\]           # capture anything between "[" and "]" into group 1
(\(                    # open group 2 and match "("
    ((?:[^()]+|(?2))+) # match anything not "(" nor ")" or recurse group 2
                       # capture the content into group 3 (the url)
\))                    # match ")" and close group 2

NOTE: The problem with this approach is that it fails for e.g. urls like

[some nasty description](https://google.com/()
#                                          ^^^

which are surely totally valid in Markdown. If you're to encounter any such urls, use a proper parser instead.

user_12314500

I think you need to distinguish between what makes a valid link in markdown, and (optionally) what is a valid url. Valid links in markdown can, for example, also be relative paths, and urls may or may not have the 'http(s)' or the 'www' part.

Your code would already work by simply using link_url = "http[s]?://.+" or even link_url = ".*". It would solve the problem of urls ending with brackets, and would simply mean that you rely on the markdown structure []() to find links . Validating urls is an entirely different discussion: How do you validate a URL with a regular expression in Python?

Example code fix:

import re

# Extract []() style links
link_name = "[^\[]+"
link_url = "http[s]?://.+"
markup_regex = f'\[({link_name})]\(\s*({link_url})\s*\)'

for match in re.findall(markup_regex, '[a link](https://www.wiki.com/atopic_(subtopic))'):
    name = match[0]
    url = match[1]
    print(url)
    # url will be https://wiki.com/atopic_(subtopic)

Note that I also adjusted link_name, to prevent problems with a single '[' somewhere in the markdown text.

user_112601850
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