Edgewall Software
Version 4 (modified by cmlenz, 8 years ago)

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Frequently Asked Questions

Here you can find answers to frequently asked questions about Markup.

What is Markup?

We like to call it a “toolkit for stream-based generation of markup for the web”. The largest feature provided by Markup is an XML-based template engine that is heavily inspired by  Kid.

Why yet another template engine?

We'll let Ryan Tomanko, the author of Kid, answer this one:

“There's at least four billion and nine text based template languages for Python but there aren't a lot of options that fit nicely into the XML tool-chain. Or, if they do fit nicely into the XML tool-chain, they don't fit nicely with Python.”

See his article  “In search of a Pythonic, XML-based Templating Language” for the details.

So then why not just use Kid?

We think that Kid represents a huge step forward for XML-based templating in Python.  Match templates and the generator-based processing model are extremely powerful concepts.

But arguably Kid also has some basic design problems. For exampe, Kid generates Python code from templates, which adds a lot of complexity to the code and can make the process of locating and fixing template errors a true nightmare. A syntax error in a template expression will cause an exception that points somewhere in the generated code. In addition, as Kid is based on  ElementTree, and the ElementTree API doesn't provide location information for parse events, exceptions reported by Kid often don't include information about what part of the template caused the error.

We felt these problems would best be addressed by developing a new engine form scratch, as opposed to trying to “fix” Kid.

What are the main differences between Kid and Markup?

Markup executes templates directly, there's no code generation phase. Expressions are evaluated in a more forgiving way by walking the AST. Template variables are stored on a stack, which means that some variable set in a loop deep in the template don't leak into the rest of the template. And even though Markup doesn't generate Python code for templates, it generally performs better than Kid (up to 2x in our tests).

Markup does not depend on ElementTree. It uses Expat for parsing XML, and is based on streaming slightly abstracted parse events through the processing pipeline. It uses XInclude (instead of Kids' py:extends) to allow template authors to factor out common bits. For match templates, it uses XPath expressions instead of the ElementTree API.

What other stuff is in the toolkit?

Beyond the template engine, Markup provides:

  • a unified stream-based processing model for markup, where
  • streams can come from XML or HTML text, or be generated programmatically using a very simple syntax.
  • XPath can be used to query any stream, not just in templates.
  • Different serialization methods (XML and HTML) for streams.
  • An HTML “sanitizing” filter to strip potentially dangerous elements or attributes from user-submitted HTML markup.