django-tag-parser

A micro-library to easily write custom Django template tags.

Features:

• Functions to parse tags, especially: "args", "kwargs", and "as varname" syntax.
• Real OOP classes to write custom inclusion tags.

Functions:

• parse_token_kwargs: split a token into the tag name, args and kwargs.
• parse_as_var: extract the "as varname" from a token.

Base classes (in tag_parser.basetags):

• BaseNode: A template Node object which features some basic parsing abilities.
• BaseInclusionNode: a Node that has inclusion_tag like behaviour, but allows to override the template_name dynamically.
• BaseAssignmentNode: a Node that returns the value in the context, using the as var syntax.
• BaseAssignmentOrOutputNode: a Node that either displays the value, or inserts it in the context.
• BaseAssignmentOrInclusionNode: a class that allows a {% get_items template="..." %} and {% get_items as var %} syntax.

The base classes allows to implement @register.simple_tag, @register.inclusion_tag and @register.assignment_tag like functionalities, while still leaving room to extend the parsing, rendering or syntax validation. For example, not all arguments need to be seen as template variables, filters or literal keywords.

As of v3.0, the @template_tag decorator is no longer needed. Use @register.tag("name") directly on the class names.

Installation

First install the module, preferably in a virtual environment. It can be installed from PyPI:

pip install django-tag-parser

Examples

At the top of your template tags library, always include the standard Django register variable and our template_tag decorator:

from django.template import Library
from tag_parser import template_tag

register = Library()

Arguments and keyword arguments

To parse a syntax like:

{% my_tag "arg1" keyword1="bar" keyword2="foo" %}

use:

from django.template import Library
from tag_parser.basetags import BaseNode

register = Library()


@register.tag('my_tag')
class MyTagNode(BaseNode):
    max_args = 1
    allowed_kwargs = ('keyword1', 'keyword2',)

    def render_tag(self, context, *tag_args, **tag_kwargs):
        return "Tag Output"

Inclusion tags

To create an inclusion tag with overwritable template_name:

{% my_include_tag "foo" template="custom/example.html" %}

use:

from django.template import Library
from tag_parser.basetags import BaseInclusionNode

register = Library()

@register.tag("my_include_tag")
class MyIncludeTag(BaseInclusionNode):
    template_name = "mytags/default.html"
    max_args = 1

    def get_context_data(self, parent_context, *tag_args, **tag_kwargs):
        (foo,) = *tag_args
        return {
            'foo': foo
        }

The get_template_name() method can be overwritten too to support dynamic resolving of template names. By default it checks the template tag_kwarg, and template_name attribute. Note the template nodes are cached afterwards, it's not possible to return random templates at each call.

Assignment tags

To create assignment tags that can either render itself, or return context data:

{% get_tags template="custom/example.html" %}
{% get_tags as popular_tags %}

use:

from django.template import Library
from tag_parser.basetags import BaseAssignmentOrInclusionNode

register = Library()


@register.tag('get_tags')
class GetPopularTagsNode(BaseAssignmentOrInclusionNode):
    template_name = "myblog/templatetags/popular_tags.html"
    context_value_name = 'tags'
    allowed_kwargs = (
        'order', 'orderby', 'limit',
    )

    def get_value(self, context, *tag_args, **tag_kwargs):
        return query_tags(**tag_kwargs)   # Something that reads the tags.

Block tags

To have a "begin .. end" block, define end_tag_name in the class:

{% my_tag keyword1=foo %}
    Tag contents, possibly other tags.
{% end_my_tag %}

use:

from django.template import Library
from tag_parser.basetags import BaseAssignmentOrInclusionNode

register = Library()


@register.tag('my_tag')
class MyTagNode(BaseNode):
    max_args = 1
    allowed_kwargs = ('keyword1', 'keyword2',)
    end_tag_name = 'end_my_tag'

    def render_tag(self, context, *tag_args, **tag_kwargs):
        # Render contents inside
        return self.nodelist.render(context)

Custom parsing

With the standard Node class from Django, it's easier to implement custom syntax. For example, to parse:

{% getfirstof val1 val2 as val3 %}

use:

from django.template import Library, Node, TemplateSyntaxError
from tag_parser import parse_token_kwargs, parse_as_var

register = Library()


@register.tag('getfirstof')
class GetFirstOfNode(Node):
    def __init__(self, options, as_var):
        self.options = options    # list of FilterExpression nodes.
        self.as_var = as_var

    @classmethod
    def parse(cls, parser, token):
        bits, as_var = parse_as_var(parser, token)
        tag_name, options, _ = parse_token_kwargs(parser, bits, allowed_kwargs=())

        if as_var is None or not choices:
            raise TemplateSyntaxError("Expected syntax: {{% {0} val1 val2 as val %}}".format(tag_name))

        return cls(options, as_var)

    def render(self, context):
        value = None
        for filterexpr in self.options:
            # The ignore_failures argument prevents that the value becomes TEMPLATE_STRING_IF_INVALID.
            value = filterexpr.resolve(context, ignore_failures=True)
            if value is not None:
                break

        context[self.as_var] = value
        return ''

Contributing

This module is designed to be generic. In case there is anything you didn't like about it, or think it's not flexible enough, please let us know. We'd love to improve it!

If you have any other valuable contribution, suggestion or idea, please let us know as well because we will look into it. Pull requests are welcome too. :-)