[Solved]-Creating a list on the fly in a Django template

by

18👍

✅

If you want to add a new variable (ie some_list), you’ll need access to the template’s context, so simple_tag won’t be enough.

For me, the first approach is to try to do this sort of work in the view, in order to keep the templates as simple as possible.

If that’s not appropriate, you’ll have to write the tag manually, like this:

@register.tag
def make_list(parser, token):
  bits = list(token.split_contents())
  if len(bits) >= 4 and bits[-2] == "as":
    varname = bits[-1]
    items = bits[1:-2]
    return MakeListNode(items, varname)
  else:
    raise template.TemplateSyntaxError("%r expected format is 'item [item ...] as varname'" % bits[0])

class MakeListNode(template.Node):
  def __init__(self, items, varname):
    self.items = map(template.Variable, items)
    self.varname = varname

  def render(self, context):
    context[self.varname] = [ i.resolve(context) for i in self.items ]
    return ""

And use it like this to create a new variable some_list:

{% make_list var1 var2 var3 as some_list %}

Feel free to give it a better name!

👤Will Hardy

3👍

I played around a bit and came up with a tag that can accept a variable number of arguments and convert them into a list. 

@register.tag('to_list')
def to_list(_parser, token):
    try:
        parts = token.split_contents()
    except ValueError:
        raise template.TemplateSyntaxError, \
          "%r tag requires at least one argument" % token.contents.split()[0]

    return AsListNode(parts[1:])

class AsListNode(template.Node):
    def __init__(self, parts):
        self.parts = map(lambda p: template.Variable(p), parts)

    def render(self, context):
        resolved = []
        for each in self.parts:
            resolved.append(each.resolve(context))
        return resolved

Template:

<p>{% to_list var1 var2 var3 %}</p>

Update

@Will’s solution is better. It lets you save the resulting list using another variable so that you can operate on it later.

👤Manoj Govindan

Leave a comment