在自定义模板标签中解析Django自定义模板标签

Question

I have a working custom template tag. I want to allow my Django admin interface users to put that template tag in a flatpage and have it render correctly. However when trying to access the rendered flatpage I get a 500 server error. The debug console prints TemplateSyntaxError: Invalid block tag: 'requesturl' . Is there some kind of custom template tag loading precedence that I am unaware of?

Here is my custom template tag:

from django import template
import requests

register = template.Library()

def getrequest(url):
    """
    Simple request object
    to GET another file
    """
    try:
        r = requests.get(url)
    except requests.exceptions.RequestException as e:
        raise IOError(e)
    except requests.exceptions.HTTPError as e:
        raise IOError(e)

    if r.status_code != 200:
        raise IOError('Non 200 response returned')
    else:
        return r.content

@register.tag(name="requesturl")
def do_requesturl(parser, token):
    """
    tag usage {% requesturl object.textfield %}
    """
    try:
        tag_name, uri = token.split_contents();
    except ValueError:
        raise template.TemplateSyntaxError, "%r tag requires a single URI string argument" % token.contents.split()[0]
    if not (uri[0] == uri[-1] and uri[0] in ('"', "'")):
        raise template.TemplateSyntaxError("%r tag's URI should be in quotes" % tag_name)
    return RequestUrlNode(uri[1:-1])

class RequestUrlNode(template.Node):
    def __init__(self, uri):
        self.uri = uri

    def render(self, context):
        try:
            pagecontent = getrequest(self.uri)
            return pagecontent
        except template.VariableDoesNotExist, template.TemplateSyntaxError:
            return 'Error rendering', self.uri

I can drop this into any of my Django templates, define a URL (in the template itself) and it uses the requests module to GET the content of the specified web page and render it in the template:

{% extends "site_layout.html" %}
{% load requesturl %}
{% requesturl "http://textfiles.com/100/914bbs.txt" %}

Great. Now, the next step is that I want my users to be able to do this in the default Django flapages app by adding the template tag in the flatpages.content field like in the screenshot below:

Note that I have ensured I am using my specific flatpages template and not the default.

To evaluate the tag I followed the steps in this SO answer . Before I tried to evaluate my own custom template tag I tested with a built-in Django template tag and filter and it worked like a charm. Below is an example of both a Django built-in template filter ( lower ) and tag ( now ):

And how it renders:

However, when I try and input my own custom template tag in, I get the dreaded TemplateSyntaxError: Invalid block tag: 'requesturl' . Below is my flatpage parsing template tag:

from django import template

register = template.Library()

@register.tag(name="evaluate")
def do_evaluate(parser, token):
    """
    tag usage {% evaluate object.textfield %}
    """
    try:
        tag_name, variable = token.split_contents()
    except ValueError:
        raise template.TemplateSyntaxError, "%r tag requires a single argument" % token.contents.split()[0]
    return EvaluateNode(variable)

class EvaluateNode(template.Node):
    def __init__(self, variable):
        self.variable = template.Variable(variable)

    def render(self, context):
        try:
            content = self.variable.resolve(context)
            t = template.Template(content)
            return t.render(context)
        except template.VariableDoesNotExist, template.TemplateSyntaxError:
            return 'Error rendering', self.variable

I'm at a loss why I can do both parts of this separately, but when I try and combine them I get the error:

File "/path/to/virtualenv/lib/python2.7/site-packages/django/template/base.py", line 332, in invalid_block_tag
raise self.error(token, "Invalid block tag: '%s'" % command)
TemplateSyntaxError: Invalid block tag: 'requesturl'

The only thing I can think of is that my custom template tag is not getting registered with Django, but then why would it work if it is embedded in the flatpages template directly? Is there some sort of underlying template tag registry or is my EvaluateNode class not doing what I think it's doing?

Thanks in advance!

Answer 1

This isn't an adequate solution in my eyes, but it is a workaround that I now have deployed. I ended up using the pre-existing Django Server Side Includes template tag {% ssi %} and including files from the file system. I had wanted my users to be able to include files outside of the system, but for my use case I can live with just including files local to the Django install.

One could argue that what I was trying to do was inherently insecure anyway, and forcing my users to only include those files that are local to the Django system is much safer. It still doesn't answer my original question which is more about custom template tag registration and use than about the actual practical use case.