Tornado has a very fast and flexible template system that is reminiscent of other template systems, such as that found in web.py.  I have found that in practical use of the template system, the documentation is thin in some areas.  A good example is in what variables and functions are exposed to the templates by default.

To that end, here is a list of the variables and functions available to a template as defined in both template.py and web.py:

• _ (underscore)
  An alias for the locale.translate() function.
• current_user
  The current_user object as returned by RequestHandler.get_current_user().
• datetime
  The datetime module.   Example: {{ datetime.date.today().year }} returns the current year.
• escape
  A function that escapes a string so it is valid within XML or XHTML.
• handler
  The request handler that called the self.render function to process the template.  Example: {{handler.static_url(‘foo’)}} will run the static_url function in RequestHandler returning a full URL path, pre-pending static_url.
• json_encode
  A function that JSON-encodes the given Python object.
• locale
  The locale value as returned by RequestHandler.get_user_locale().
• request
  The request object that is passed into the Request Handler.
• reverse_url 
  Given a full module and class (myapp.Homepage) it will look at the handler to URI mapping and return the URL for the given class.
• squeeze
  A function that replaces all sequences of whitespace chars with a single space.
• static_url
  The value of the static_url property passed in to the application settings.
• url_escape
  A function that returns a valid URL-encoded version of the given value.
• xsrf_form_html
  If using the cross-site forgery protection, this function returns the hidden input field containing the xrsf variable.