Custom Template Tags Don't Work about django-2-web-development-cookbook-third-edition

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The context received here should be that which is given from the template itself. What should happen is that:

• the developer provides context to the tag as either a string literal:

  {% try_to_include "path/to/template.html" %}

  or some variable:

  {% try_to_include context %}

• the tag is initialized with a template.Variable() that will look for the "template_name" property in some context, when resolved
• upon rendering, the context, which was given as the argument, is used to attempt to resolve the template_name
  • if the context was a literal string, the result is the same literal string
  • if the context was a string variable, the result is that string
  • if the context was an object or dict containing a resolvable "template_name" property or key, the corresponding value is the result
• the result is then used when we get_template() by name
  • if the template is found, then we render() it and the resulting string is returned
  • upon expected template.TemplateDoesNotExist, template.VariableDoesNotExist, or AttributeError, the rendering given is an empty string
  • other raised exceptions will cause the tag to fully error out

The only reason you should receive a RequestContext in the IncludeNode's render() would be if that is the context passed from the template itself.