Ch4 Templates8/29/2015

Templates

• Using the Template System• Basic Template Tags and Filters• Template Loading• Template Inheritance

This Django template describes an HTML page

Using the Template System

1. Create a Template object by providing the raw template code as a string.

2. Call the render() method of the Template object with a given set of variables (the context). This returns a fully rendered template as a string, with all of the variables and template tags evaluated according to the context.

Creating Template Objects

The easiest way to create a Template object is to instantiate it directly. Running python manage.py shell instead of just python.

The system raises a TemplateSyntaxError exception for any of the following cases ： Invalid tags Invalid arguments to valid tags Invalid filters Invalid arguments to valid filters Invalid template syntax Unclosed tags (for tags that require closing tags)

Rendering a Template

Multiple Contexts, Same Template

Context Variable Lookup

1. Dictionary lookup (e.g., foo["bar"])

2. Attribute lookup (e.g., foo.bar)

3. Method call (e.g., foo.bar())

4. List-index lookup (e.g., foo[2])

• Method Call Behavior

• If, during the method lookup, a method raises an exception, the exception will be propagated, unless the exception has an attribute silent_variable_failure whose value is True. If the exception does have a silent_variable_failure attribute, the variable will render as an empty string.

• A method call will only work if the method has no required arguments. Otherwise, the system will move to the next lookup type (list-index lookup).

• Some methods have side effects, and it would be foolish at best, and possibly even a security hole, to allow the template system to access them.

• How Invalid Variables Are Handled

• If a variable doesn’t exist, the template system renders it as an empty string, failing silently.

Playing with Context Objects

A context is simply a set of template variable names and their associated values.

Most of the time, you’ll instantiate Context objects by passing in a fully populated dictionary to Context(). But you can add and delete items from a Context object once it’s been instantiated, too,

Basic Template Tags and Filters

Tag• if / else

And, Or, Not, elif• for

forloop.counter forloop.counter0 forloop.revcounter forloop.revcounter0 forloop.first forloop.last forloop.parentloop

• ifequal / ifnotequal• comments

Invalid examples

An empty list ([])An empty tuple (())An empty dictionary ({})An empty string ('')Zero (0)The special object NoneThe object False (obviously)Custom objects that define their own Boolean context behavior (this is advanced Python usage)

False in a Boolean context

Filter• {{ name|lower }} ： Do not put any space

character before and after the pipe.• {{ my_list|first|upper }} ： Filters can be

chained.• {{ bio|truncatewords:"30" }} ： Double

quotes only.• {{ pub_date|date:"F j, Y" }}

Template Loading

Template Loading

• render_to_response()• The locals() Trick• Subdirectories in get_template()• The include Template Tag

Template Inheritance

1. Create a base.html template that holds the main look and feel of your site.

2. Create a base_SECTION.html template for each “section” of your site (e.g., base_photos.html and base_forum.html).

3. Create individual templates for each type of page, such as a forum page or a photo gallery.

Template Inheritance

HsuanWen Liu

“Thank you.”