Python html5lib Skipped Elements

By  on  

I've been working on some interesting python stuff at Mozilla and one task recently called for called for rending a page and then finding elements with a URL attribute value (like img[src] or a[href]) and ensuring they become absolute URLs.  One problem I encountered when using html5lib was that LINK and IMG elements were being skipped when I tokenized the HTML.  After browsing through the html5lib source code, I found a variable called voidElements which included both LINK and IMAGE:

voidElements = frozenset((
    "base",
    "command",
    "event-source",
    "link",
    "meta",
    "hr",
    "br",
    "img",
    "embed",
    "param",
    "area",
    "col",
    "input",
    "source"
))

When I commented out those two elements, they were found upon next run of my routine, meaning their presence in the set were causing me problems.  Here's how I skirted the issue:

new_void_set = set()
for item in html5lib_constants.voidElements:
	new_void_set.add(item)
new_void_set.remove('link')
new_void_set.remove('img')
html5lib_constants.voidElements = frozenset(new_void_set)

Since voidElements is a frozenset, I couldn't simply remove LINK and IMG, so I needed to create a new frozenset without those elements.  Let me know if there's a more python-ish way of creating this frozen set.  In an event, delving into the deep recesses of html5lib paid off and I accomplished the goal!

Recent Features

  • By
    Send Text Messages with PHP

    Kids these days, I tell ya.  All they care about is the technology.  The video games.  The bottled water.  Oh, and the texting, always the texting.  Back in my day, all we had was...OK, I had all of these things too.  But I still don't get...

  • By
    How I Stopped WordPress Comment Spam

    I love almost every part of being a tech blogger:  learning, preaching, bantering, researching.  The one part about blogging that I absolutely loathe:  dealing with SPAM comments.  For the past two years, my blog has registered 8,000+ SPAM comments per day.  PER DAY.  Bloating my database...

Incredible Demos

  • By
    Display Images as Grayscale with CSS Filters

    CSS filters aren't yet widely supported but they are indeed impressive and a modern need for web imagery.  CSS filters allow you to modify the display of images in a variety of ways, one of those ways being displaying images as grayscale. Doing so requires the...

  • By
    Degradable SELECT onChange

    Whenever I go to Google Analytics I notice a slight flicker in the dropdown list area. I see a button appear for the shortest amount of time and the poof! Gone. What that tells me is that Google is making their site function...

Discussion

  1. You could use list comprehension to filter the elements instead; something like:

    html5lib_constants.voidElements = frozenset([e for e in html5lib_constants.voidElements if e not in [“link”, “img”]])

    Sounds like it would be useful to add void element overriding as a feature to the library in the future, though.

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!