django框架模板中定义变量(set variable in django template)的方法分析

{% with total=business.employees.count %}
  {{ total }} employee{{ total|pluralize }}
{% endwith %}

{%with age=100%}
{{ age|add:"2" }}
....
{%with%}

from django import template
register = template.Library()
class SetVarNode(template.Node):
  def __init__(self, var_name, var_value):
    self.var_name = var_name
    self.var_value = var_value
  def render(self, context):
    try:
      value = template.Variable(self.var_value).resolve(context)
    except template.VariableDoesNotExist:
      value = ""
    context[self.var_name] = value
    return u""
def set_var(parser, token):
  """
    {% set <var_name> = <var_value> %}
  """
  parts = token.split_contents()
  if len(parts) < 4:
    raise template.TemplateSyntaxError("'set' tag must be of the form: {% set <var_name> = <var_value> %}")
  return SetVarNode(parts[1], parts[3])
register.tag('set', set_var)

{% load set_var %}
{% set a = 3 %}
{% set b = some_context_variable %}
{% set c = "some string" %}