Defining “global variable” in Django templates

Question

I\'m doing something like:

{% extends \'base.html\' %}
{% url myapp.views.dashboard object as object_url %}
{% block sidebar %}
... {{ object_url }} ...
{% e         


        

Answer 1

Looks like this was answered before, but there is an alternative. It's one thing to use a context processor to keep track of something defined from outside the template, but sometimes you want to count the number of times two loops go through, or something like that. There is another way:

class GlobalVariable(object):
    def __init__(self, varname, varval):
        self.varname = varname
        self.varval = varval

    def name(self):
        return self.varname

    def value(self):
        return self.varval

    def set(self, newval):
        self.varval = newval


class GlobalVariableSetNode(template.Node):
    def __init__(self, varname, varval):
        self.varname = varname
        self.varval = varval

    def render(self, context):
        gv = context.get(self.varname, None)
        if gv:
            gv.set(self.varval)
        else:
            gv = context[self.varname] = GlobalVariable(
                self.varname, self.varval)
        return ''


def setglobal(parser, token):
    try:
        tag_name, varname, varval = token.contents.split(None, 2)
    except ValueError:
        raise template.TemplateSyntaxError(
            "%r tag requires 2 arguments" % token.contents.split()[0])
    return GlobalVariableSetNode(varname, varval)


register.tag('setglobal', setglobal)


class GlobalVariableGetNode(template.Node):
    def __init__(self, varname):
        self.varname = varname

    def render(self, context):
        try:
            return context[self.varname].value()
        except AttributeError:
            return ''


def getglobal(parser, token):
    try:
        tag_name, varname = token.contents.split(None, 1)
    except ValueError:
        raise template.TemplateSyntaxError(
            "%r tag requires arguments" % token.contents.split()[0])
    return GlobalVariableGetNode(varname)


register.tag('getglobal', getglobal)


class GlobalVariableIncrementNode(template.Node):
    def __init__(self, varname):
        self.varname = varname

    def render(self, context):
        gv = context.get(self.varname, None)
        if gv is None:
            return ''
        gv.set(int(gv.value()) + 1)
        return ''


def incrementglobal(parser, token):
    try:
        tag_name, varname = token.contents.split(None, 1)
    except ValueError:
        raise template.TemplateSyntaxError(
            "%r tag requires arguments" % token.contents.split()[0])
    return GlobalVariableIncrementNode(varname)


register.tag('incrementglobal', incrementglobal)

This allows you to use it in a template like this:

{% setglobal ii 0 %}
...
{% for ... %}
  {% incrementglobal ii %}
  current={% getglobal ii %}
{% endfor %}
...
{% for ... %}
  {% incrementglobal ii %}
  current={% getglobal ii %}
{% endfor %}
...
total of 2 loops={% getglobal ii %}
...
{% setglobal ii 0 %}
...
do something else now that {% getglobal ii %} is back to 0