Custom template tags

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To mark the output as a safe string, use django. Be careful, though. You need to do more than just mark the output as safe. You need to ensure it really is safe, and what you do depends on whether auto-escaping is in effect.

The idea is to write filters that can operate in templates where auto-escaping is either on or off in order to make things easier for your template authors. This flag tells Django that your filter function wants to be passed an extra keyword argument, called autoescape , that is True if auto-escaping is in effect and False otherwise.

It is recommended to set the default of the autoescape parameter to True , so that if you call the function from Python code it will have escaping enabled by default. We use autoescape to decide whether the input data needs to be passed through django.

Finally, in the above example, we remember to mark the result as safe so that our HTML is inserted directly into the template without further escaping. When this flag is set, if the first argument to your filter is a time zone aware datetime, Django will convert it to the current time zone before passing it to your filter when appropriate, according to rules for time zones conversions in templates. Tags are more complex than filters, because tags can do anything. Django provides a number of shortcuts that make writing most types of tags easier.

Many template tags take a number of arguments — strings or template variables — and return a result after doing some processing based solely on the input arguments and some external information. This function, which is a method of django. Library , takes a function that accepts any number of arguments, wraps it in a render function and the other necessary bits mentioned above and registers it with the template system.

Note that the first argument must be called context. For example:. Then in the template any number of arguments, separated by spaces, may be passed to the template tag. This is done by using the as argument followed by the variable name. Doing so enables you to output the content yourself where you see fit:. Another common type of template tag is the type that displays some data by rendering another template. Writing inclusion tags is probably best demonstrated by example. First, define the function that takes the argument and produces a dictionary of data for the result.

The important point here is we only need to return a dictionary, not anything more complex. This will be used as a template context for the template fragment. This template is a fixed feature of the tag: the tag writer specifies it, not the template designer. Following our example, the template is very short:. Following our example, if the above template is in a file called results.

Alternatively it is possible to register the inclusion tag using a django. Template instance:. Sometimes, your inclusion tags might require a large number of arguments, making it a pain for template authors to pass in all the arguments and remember their order.

Note that the first parameter to the function must be called context. In that register. Then, any time you want to use that custom tag, load its library and call it without any arguments, like so:. It automatically gets access to the context. The template system works in a two-step process: compiling and rendering.

To define a custom template tag, you specify how the compilation works and how the rendering works. Each node is an instance of django. Node and has a render method. A compiled template is a list of Node objects. When you call render on a compiled template object, the template calls render on each Node in its node list, with the given context. The results are all concatenated together to form the output of the template.

For each template tag the template parser encounters, it calls a Python function with the tag contents and the parser object itself. This function is responsible for returning a Node instance based on the contents of the tag.