Hext — Extract Data from HTML

Hext is a domain-specific language for extracting structured data from HTML. It can be thought of as a counterpart to templates, which are typically used by web developers to structure content on the web.

A Quick Example

The following Hext template collects all hyperlinks and extracts the href and the clickable text.

<a href:link @text:title />

Hext does so by recursively trying to match every HTML element. In the case above, an element is required to have the tag a and an attribute called href. If the element matches, its attribute href and its textual representation are stored as link and title, respectively.

If the above Hext template is applied to this piece of HTML:

<body>
  <a href="one.html">  Page 1</a>
  <a href="two.html">  Page 2</a>
  <a href="three.html">Page 3</a>
</body>

Hext will produce the following values:

{ "link": "one.html",   "title": "Page 1" },
{ "link": "two.html",   "title": "Page 2" },
{ "link": "three.html", "title": "Page 3" }

You can use this example in Hext’s live code editor. Visit Hext’s documentation and its section “How Hext Matches Elements” for a more thorough explanation.

Components

This package includes:

• The Hext Python module
• The htmlext command-line utility

Using Hext with Python

The module exposes three interfaces:

• html = hext.Html("<html>...</html>") -> object
• rule = hext.Rule("...") -> object
• rule.extract(html) -> dictionary of {string -> string}
• rule.extract has a second optional parameter max_searches which is of type unsigned int. The search for matching elements is aborted after this limit is reached. The default is 0, which never aborts.

import hext
import requests
import json

res = requests.get('https://news.ycombinator.com/')
res.raise_for_status()

# hext.Html's constructor expects a single argument
# containing an UTF-8 encoded string of HTML.
html = hext.Html(res.text)

# hext.Rule's constructor expects a single argument
# containing a Hext template.
# Throws an exception of type ValueError on invalid syntax.
rule = hext.Rule("""
<tr>
  <td><span @text:rank /></td>
  <td><a href:href @text:title /></td>
</tr>
<?tr>
  <td>
    <span @text:score />
    <a @text:user />
    <a:last-child @text:filter(/\d+/):comment_count />
  </td>
</tr>""")

# hext.Rule.extract expects an argument of type hext.Html.
# Returns a list of dictionaries.
result = rule.extract(html)

# Print each dictionary as JSON
for map in result:
    print(json.dumps(map, ensure_ascii=False,
                          separators=(',',':')))

Using Hext on the Command Line

Hext ships with a command line utility called htmlext, which applies Hext templates to HTML documents and outputs JSON.

htmlext - Extract structured content from HTML.

Usage:
  htmlext [options] <hext-file> <html-file...>
      Apply extraction rules from <hext-file> to each
      <html-file> and print the captured content as JSON.

Options:
  -x [ --hext ] <file>  Add Hext from file
  -i [ --html ] <file>  Add HTML from file
  -s [ --str ] <string> Add Hext from string
  -c [ --compact ]      Print one JSON object per line
  -p [ --pretty ]       Pretty-print JSON
  -a [ --array ]        Wrap results in a JSON array
  -f [ --filter ] <key> Print values whose name matches <key>
  -l [ --lint ]         Do Hext syntax check
  -h [ --help ]         Print this help message
  -V [ --version ]      Print info and version

Ever wanted to watch the submissions on /r/videos in vlc? Well, take a look at this little guy right here:

htmlext \
  -i <(wget -O- -o/dev/null "https://old.reddit.com/r/videos/") \
  -s '<a class="title" href:x />' \
  -f x \
  | xargs vlc

License

Hext is released under the terms of the Apache License v2.0. The source code is hosted on Github. This binary package includes content authored by third parties:

• gumbo-parser. Copyright 2010 Google Inc. See gumbo.license.
• rapidjson. Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. See rapidjson.license.