Miscellaneous features

URLs

For URL handling XIST uses the module ll.url. Refer to its documentation for the basic functionality (especially regarding the methods __div__() and and ll.url.URL.relative().

When XIST parses an XML resource it uses a so called “base” URL. This base URL can be passed to all parsing functions. If it isn’t specified it defaults to the URL of the resource being parsed. This base URL will be prepended to all URLs that are read during parsing:

>>> from ll.xist import parse
>>> from ll.xist.ns import html
>>> node = parse.parsestring('<img src="eggs.png"/>', base="root:spam/index.html")
>>> print node.string()
<img src="root:spam/eggs.png" />

For publishing a base URL can be specified too. URLs will be published relative to this base URL with the exception of relative URLs in the tree. This means:

When you have a relative URL (e.g. #top) generated by a convert() call, this URL will stay the same when publishing.
Base URLs for parsing should never be relative: Relative base URLs will be prepended to all relative URLs in the file, but this will not be reverted for publishing. In most cases the base URL should be a root URL when you parse local files.
When you parse remote web pages you can either omit the base argument, so it will default to the URL being parsing, so that links, images, etc. on the page will still point back to their original location, or you might want to use the empty URL URL() as the base, so you’ll get all URLs in the page as they are.
When XIST is used as a compiler for static pages, you’re going to read source XML files, do a conversion and write the result to a new target file. In this case you should probably use the URL of the target file for both parsing and publishing. Let’s assume we have an URL #top in the source file. When we use the “real” file names for parsing and publishing like this:
```
node = parse.parsefile("spam.htmlxsc", base="root:spam.htmlxsc")
node = node.conv()
node.write(open("spam.html", "wb"), base="root:spam.html")
```
the following will happen: The URL #top will be parsed as root:spam.htmlxsc#top. After conversion this will be written to spam.html relative to the URL root:spam.html, which results in spam.html#top, which works, but is not what you want.

When you use root:spam.html both for parsing and publishing, #top will be written to the target file as expected.

Pretty printing XML

The method pretty() can be used for pretty printing XML. It returns a new version of the node, with additional white space between the elements:

from ll.xist.ns import html
node = html.html(
   html.head(
      html.title("foo"),
   ),
   html.body(
      html.div(
         html.h1("The ", html.em("foo"), " page!"),
         html.p("Welcome to the ", html.em("foo"), " page."),
      ),
   ),
)

print node.pretty().bytes()

This will print:

<html>
   <head>
      <title>foo</title>
   </head>
   <body>
      <div>
         <h1>The <em>foo</em> page!</h1>
         <p>Welcome to the <em>foo</em> page.</p>
      </div>
   </body>
</html>

Element content will only be modified if it doesn’t contain Text nodes, so mixed content will not be touched.

Automatic generation of image size attributes

The module ll.xist.ns.htmlspecials contains an element autoimg that extends img. When converted to HTML via the convert() method the size of the image will be determined and the height and width attributes will be set accordingly (if those attributes are not set already).

Embedding Python code

It’s possible to embed Python code into XIST XML files. For this XIST supports two new processing instructions: pyexec and :class:~`ll.xist.ns.code.pyeval` (in the module ll.xist.ns.code). The content of pyexec will be executed when the processing instruction node is converted.

The result of a call to convert() for a :class:~`ll.xist.ns.code.pyeval` processing instruction is whatever the Python code in the content returns. The processing instruction content is treated as the body of a function, so you can put multiple return statements there. The converter is available as the parameter converter inside the processing instruction. For example, consider the following XML file:

<?pyexec
   # sum
   def gauss(top=100):
      sum = 0
      for i in range(top+1):
         sum += i
      return sum
?>
<b><?pyeval return gauss()?></b>

Parsing this file and calling convert() results in the following:

<b>5050</b>