DjangoBook Chapter 4: Templates

1. Ch4 Templates
8/29/2015

2. Templates
• Using the Template System
• Basic Template Tags and Filters
• Template Loading
• Template Inheritance

3. This Django template
describes an HTML page

4. Using the Template System

5. 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.

6. 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)

7. Rendering a Template

8. Multiple Contexts, Same
Template

9. 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])

10. • 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.

11. 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,

12. Basic Template Tags
and Filters

13. 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

14. An empty list ([])
An empty tuple (())
An empty dictionary ({})
An empty string ('')
Zero (0)
The special object None
The object False (obviously)
Custom objects that define their own Boolean context
behavior (this is advanced Python usage)
False in a Boolean context

15. 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" }}

16. Template Loading

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

18. Template Inheritance

19. 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

20. HsuanWen Liu
“Thank you.”