A tag that injects any output of another template tag into current context. Syntax: `{% inject as variable_name from tag_name [tag_arg ...] %}` where `variable_name` if the key to inject into, `tag_name` is the name of tag to retrieve value from, and `tag_arg`s are parameters to be used in the tag specified by `tag_name`.

injection.py

from django.template import (
    TemplateSyntaxError, Library, Node, Variable, Token, TOKEN_BLOCK
)


register = Library()


@register.tag(name='inject')
def inject(parser, token):
    """
    A tag that injects any output of another template tag into current context.
    Syntax: `{% inject as variable_name from tag_name [tag_arg ...] %}` where
    `variable_name` if the key to inject into, `tag_name` is the name of tag to
    retrieve value from, and `tag_arg`s are parameters to be used in the tag
    specified by `tag_name`.

    Example usage:
        {% inject "result" from "now" "jS F Y H:i" %}
        It is {{ result }}.
    """
    parts = token.split_contents()
    name = parts[0]
    var_name = parts[1]
    if parts[2] != 'from':
        syntax_error_msg = (
            '{name} tag requires syntax `{name} as <variable_name> from '
            '<tag_name> [tag_args ...]`'
        ).format(name=name)
        TemplateSyntaxError(syntax_error_msg)
    tag_name = parts[3]
    return InjectNode(tag_name, var_name, parser, parts[4:])


class InjectNode(Node):
    def __init__(self, tag_name, var_name, parser, parts):
        super(InjectNode, self).__init__()
        self.var_name = var_name
        self.tag_name = tag_name
        self.parts = parts
        self.parser = parser

    def render(self, context):
        tag_name = Variable(self.tag_name).resolve(context)
        tag = self.parser.tags.get(tag_name, None)
        self.parts.insert(0, tag_name)
        token = Token(TOKEN_BLOCK, ' '.join(self.parts))
        result = tag(self.parser, token).render(context)
        var_name = Variable(self.var_name).resolve(context)
        context[var_name] = result
        return ''