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take-dsl

A DSL for extracting data from a web page.

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A DSL for extracting data from a web page. The DSL serves two purposes: finds elements and extracts their text or attribute values. The main reason for developing this is to have all the CSS selectors for scraping a site in one place (I prefer CSS selectors over anything else).

The DSL wraps cheerio in node and jQuery in the browser.

A few links:

Example

Given the following take template:

$ h1 | text
    save: h1_title
$ ul
    save each: uls
        $ li
            | 0 [title]
                save: title
            | 1 text
                save: second_li
$ p | 1 text
    save: p_text

And the following HTML:

<div>
    <h1>Le Title 1</h1>
    <p>Some body here</p>
    <h2 class="second title">The second title</h2>
    <p>Another body here</p>
    <ul id="a">
        <li title="a less than awesome title">A first li</li>
        <li>A second li</li>
        <li>A third li</li>
    </ul>
    <ul id="b">
        <li title="some awesome title">B first li</li>
        <li>B second li</li>
        <li>B third li</li>
    </ul>
</div>

The following data will be extracted (presented in JSON format):

{
    "h1_title": "Le Title 1",
    "p_text": "Another body here",
    "uls": [
        {
            "title": "a less than awesome title",
            "second_li": "A second li"
        },
        {
            "title": "some awesome title",
            "second_li": "B second li"
        }
    ]
}

Take templates always result in a single JavaScript Object.

The template can also be written in the following, more concise, syntax:

$ h1 | text ;                   : h1_title
$ ul
    save each                   : uls
        $ li
            | 0 [title] ;           : title
            | 1 text ;              : second_li
$ p | 1 text ;                  : p_text

For a more complex example, see the reddit sample, which also has a more concise version.

Install

Node

npm  install take-dsl

Browser

Include the web_dist script in your page. If your page has jQuery loaded, you should be good to go. See the web_dist/index.html for a dead-simple demo. It can be served via npm start.

Usage

Creating a Take Template

A take template is created from an Array of strings with each string being one line of the take template.

To create a template:

var TakeTemplate = require('take-dsl').TakeTemplate,
    TMPL = [
        '$ nav a',
        '    save each: nav',
        '        | text',
        '            save: text',
        '        | [href]',
        '            save: link'
    ],
    tt = new TakeTemplate(TMPL);

Using a Take Template

Pass a HTML string to the .take() method:

data = tt.take('<div>hello world</div>')

Take Templates

Take templates are whitespace sensitive and are comprised of three types of lines:

  • Queries
    • $ h1
    • | text
    • $ h1 | 0 text
  • save directives
    • save: h1_title
    • save: time.exact
  • save each directives
    • save each: entries
    • save each: popular.movies

There are also inline sub-contexts, which are described in the Inline Sub-Contexts section.

Queries

There are two main types of queries in take templates:

  • CSS selector queries
  • Non-CSS selector queries

The reason they’re divided like this is because CSS Selectors always go first on the line and they can be followed by non-CSS non-CSS Selector queries. Non-CSS selector queries can’t be followed by CSS selector queries. Seems easier to read this way, but it’s arbitrary and the syntax can be changed if something else makes more sense.

CSS Selector queries

CSS selector queries start with $ and end either at the end of the line or at the | character. The | character delimits non-CSS selector queries.

  • $ #siteTable .thing | text
  • $ .domain a

In the first example above, the CSS selector query is #siteTable .thing. The second is .domain a.

The CSS selectors are passed to cheerio in node and jQuery in the browser (jQuery is an external dependency in the browser distribution). So, anything cheerio or jQuery can accept can be used.

Non-CSS Selector queries

Non-CSS selector queries start with | and continue for the rest of the line. There are three non-CSS Selector queries:

  • Element indexes
    • Syntax: an integer
    • | 0 will return the first element in the current context
    • | 1 will return the second element in the current context
  • Text retrieval
    • Syntax: text
    • | text will return the text of the current context
    • | 1 text will first get the second element in the current context and then return it’s text
  • Attribute retrieval
    • Syntax: [attr]
    • | [href] will return the value of the href attribute of the first element in the current context
    • | 1 [href] will return the value of the href attribute of the second element in the current context

Order matters: Index queries should precede text or attribute retrieval queries. Only one of text or attribute queries can be used; they can’t both be used on one line.

Whitespace

The level of indentation on each line defines the context for the line.

The root context of a take template is the current HTML document being processed. Every statement that is not indented is executed against the document being processed.

Each line that is indented more deeply has a context that is the result of the last query in the parent context. For example:

$ #some-id
    $ li
    $ div

The query on the first line is executed against the document being processed. The query on the second line is executed against the result of the first line. So, the second line is synonomous with $ #some-id li. The query on the third line is also executed against the result of the first line. So, it can be re-written as $ #some-id div.

Another example:

$ a
    | 0
        | text
        | [href]

The third and fourth lines retrieve the text and href attribute, respectively, from the first <a> in the document being processed. This could be rewritten as:

$ a | 0
    | text
    | [href]

Save Directives

Save directives save the context into the result Object. These are generally only intended to be applied to the result of a text or [attr] retrieval.

The syntax is:

save: identifier

Any non-whitespace characters can be used as the identifier. Also, the identifier can contain dots (.), which designate sub-Objects for saving.

For example, the following take template:

$ a | 0
    | text
        save: first_a.text
    | [href]
        save: first_a.href

And the following HTML:

<div>
    <a href="http://www.example.com">fo sho</a>
    <a href="http://www.another.com">psych out</a>
</div>

Will result in the following Object:

{
    first_a: {
        text: 'fo sho',
        href: 'http://www.example.com'
    }
}

Save Each Directives

Save each directives produce an Array of Objects. Generally, these are used for repeating elements on a page. In the reddit sample, a save each directive is used to save each of the reddit entries on the reddit homepage.

The syntax is:

save each: identifier

Any non-whitespace characters can be used as the identifier. Also, the identifier can contain dots (.), which designate sub-Objects for saving.

Save each directives apply the next sub-context to each of the elements of their context. Put another way, save each directives repeatedly process each element of thier context.

For example, in the following take template, the | text and | [href] queries (along with saving the results) will be applied to every <a> in the document.

$ a
    save each: anchors
        | text
            save: text
        | [href]
            save: href

Applying the above take template to the following HTML:

<div>
    <a href="http://www.example.com">fo sho</a>
    <a href="http://www.another.com">psych out</a>
</div>

Will result in the following Object:

{
    anchors: [{
            text: 'fo sho',
            href: 'http://www.example.com'
        },{
            text: 'psych out',
            href: 'http://www.another.com'
        }
    ]
}

Inline Sub Contexts

Very often take templates contain statements like the following:

$ h1 | text
    save: section_title

Inline sub-contexts can make statements like these more succinct. Inline sub-contexts allow you to create a sub-context on the same line as a query.

The syntax is:

query ; sub-context-statement

For example, the template above that saves the h1 text can be re-written as:

$ h1 | text ; save: section_title

This can be handy for larger templates. The sample at the beginning of this document becomes:

$ h1 | text ;                   : h1_title
$ ul
    save each                   : uls
        $ li
            | 0 [title] ;           : title
            | 1 text ;              : second_li
$ p | 1 text ;                  : p_text

For additional samples with inline sub-contexts, see the stackoverflow example which scrapes user activity for questions on stackoverflow.com. The example uses the Python package, but the syntax of the templates is identical.

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