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tornado.template — Flexible output generation

A simple template system that compiles templates to Python code.

Basic usage looks like:

t = template.Template("<html>{{ myvalue }}</html>")

Loader is a class that loads templates from a root directory and caches the compiled templates:

loader = template.Loader("/home/btaylor")

We compile all templates to raw Python. Error-reporting is currently… uh, interesting. Syntax for the templates:

### base.html
    <title>{% block title %}Default title{% end %}</title>
      {% for student in students %}
        {% block student %}
          <li>{{ escape( }}</li>
        {% end %}
      {% end %}

### bold.html
{% extends "base.html" %}

{% block title %}A bolder title{% end %}

{% block student %}
  <li><span style="bold">{{ escape( }}</span></li>
{% end %}

Unlike most other template systems, we do not put any restrictions on the expressions you can include in your statements. if and for blocks get translated exactly into Python, so you can do complex expressions like:

{% for student in [p for p in people if p.student and p.age > 23] %}
  <li>{{ escape( }}</li>
{% end %}

Translating directly to Python means you can apply functions to expressions easily, like the escape() function in the examples above. You can pass functions in to your template just like any other variable (In a RequestHandler, override RequestHandler.get_template_namespace):

### Python code
def add(x, y):
   return x + y

### The template
{{ add(1, 2) }}

We provide the functions escape(), url_escape(), json_encode(), and squeeze() to all templates by default.

Typical applications do not create Template or Loader instances by hand, but instead use the render and render_string methods of tornado.web.RequestHandler, which load templates automatically based on the template_path Application setting.

Variable names beginning with _tt_ are reserved by the template system and should not be used by application code.

Syntax Reference

Template expressions are surrounded by double curly braces: {{ ... }}. The contents may be any python expression, which will be escaped according to the current autoescape setting and inserted into the output. Other template directives use {% %}.

To comment out a section so that it is omitted from the output, surround it with {# ... #}.

These tags may be escaped as {{!, {%!, and {#! if you need to include a literal {{, {%, or {# in the output.

{% apply *function* %}...{% end %}

Applies a function to the output of all template code between apply and end:

{% apply linkify %}{{name}} said: {{message}}{% end %}

Note that as an implementation detail apply blocks are implemented as nested functions and thus may interact strangely with variables set via {% set %}, or the use of {% break %} or {% continue %} within loops.

{% autoescape *function* %}

Sets the autoescape mode for the current file. This does not affect other files, even those referenced by {% include %}. Note that autoescaping can also be configured globally, at the Application or Loader.:

{% autoescape xhtml_escape %}
{% autoescape None %}
{% block *name* %}...{% end %}

Indicates a named, replaceable block for use with {% extends %}. Blocks in the parent template will be replaced with the contents of the same-named block in a child template.:

<!-- base.html -->
<title>{% block title %}Default title{% end %}</title>

<!-- mypage.html -->
{% extends "base.html" %}
{% block title %}My page title{% end %}
{% comment ... %}
A comment which will be removed from the template output. Note that there is no {% end %} tag; the comment goes from the word comment to the closing %} tag.
{% extends *filename* %}
Inherit from another template. Templates that use extends should contain one or more block tags to replace content from the parent template. Anything in the child template not contained in a block tag will be ignored. For an example, see the {% block %} tag.
{% for *var* in *expr* %}...{% end %}
Same as the python for statement. {% break %} and {% continue %} may be used inside the loop.
{% from *x* import *y* %}
Same as the python import statement.
{% if *condition* %}...{% elif *condition* %}...{% else %}...{% end %}
Conditional statement - outputs the first section whose condition is true. (The elif and else sections are optional)
{% import *module* %}
Same as the python import statement.
{% include *filename* %}
Includes another template file. The included file can see all the local variables as if it were copied directly to the point of the include directive (the {% autoescape %} directive is an exception). Alternately, {% module Template(filename, **kwargs) %} may be used to include another template with an isolated namespace.
{% module *expr* %}

Renders a UIModule. The output of the UIModule is not escaped:

{% module Template("foo.html", arg=42) %}

UIModules are a feature of the tornado.web.RequestHandler class (and specifically its render method) and will not work when the template system is used on its own in other contexts.

{% raw *expr* %}
Outputs the result of the given expression without autoescaping.
{% set *x* = *y* %}
Sets a local variable.
{% try %}...{% except %}...{% else %}...{% finally %}...{% end %}
Same as the python try statement.
{% while *condition* %}... {% end %}
Same as the python while statement. {% break %} and {% continue %} may be used inside the loop.
{% whitespace *mode* %}
Sets the whitespace mode for the remainder of the current file (or until the next {% whitespace %} directive). See filter_whitespace for available options. New in Tornado 4.3.

Class reference

class tornado.template.Template(template_string, name="<string>", loader=None, compress_whitespace=None, autoescape="xhtml_escape", whitespace=None)[source]

A compiled template.

We compile into Python from the given template_string. You can generate the template from variables with generate().

Construct a Template.

  • template_string (str) – the contents of the template file.
  • name (str) – the filename from which the template was loaded (used for error message).
  • loader (tornado.template.BaseLoader) – the BaseLoader responsible for this template, used to resolve {% include %} and {% extend %} directives.
  • compress_whitespace (bool) – Deprecated since Tornado 4.3. Equivalent to whitespace="single" if true and whitespace="all" if false.
  • autoescape (str) – The name of a function in the template namespace, or None to disable escaping by default.
  • whitespace (str) – A string specifying treatment of whitespace; see filter_whitespace for options.

Changed in version 4.3: Added whitespace parameter; deprecated compress_whitespace.


Generate this template with the given arguments.

class tornado.template.BaseLoader(autoescape='xhtml_escape', namespace=None, whitespace=None)[source]

Base class for template loaders.

You must use a template loader to use template constructs like {% extends %} and {% include %}. The loader caches all templates after they are loaded the first time.

Construct a template loader.

  • autoescape (str) – The name of a function in the template namespace, such as “xhtml_escape”, or None to disable autoescaping by default.
  • namespace (dict) – A dictionary to be added to the default template namespace, or None.
  • whitespace (str) – A string specifying default behavior for whitespace in templates; see filter_whitespace for options. Default is “single” for files ending in “.html” and “.js” and “all” for other files.

Changed in version 4.3: Added whitespace parameter.


Resets the cache of compiled templates.

resolve_path(name, parent_path=None)[source]

Converts a possibly-relative path to absolute (used internally).

load(name, parent_path=None)[source]

Loads a template.

class tornado.template.Loader(root_directory, **kwargs)[source]

A template loader that loads from a single root directory.

class tornado.template.DictLoader(dict, **kwargs)[source]

A template loader that loads from a dictionary.

exception tornado.template.ParseError(message, filename=None, lineno=0)[source]

Raised for template syntax errors.

ParseError instances have filename and lineno attributes indicating the position of the error.

Changed in version 4.3: Added filename and lineno attributes.

tornado.template.filter_whitespace(mode, text)[source]

Transform whitespace in text according to mode.

Available modes are:

  • all: Return all whitespace unmodified.
  • single: Collapse consecutive whitespace with a single whitespace character, preserving newlines.
  • oneline: Collapse all runs of whitespace into a single space character, removing all newlines in the process.

New in version 4.3.