code: def render_template_to_string(input, _from_string=False, **context):
      
      if _from_string:
          template = current_app.jinja_env.from_string(input)
      else:
          template = current_app.jinja_env.get_or_select_template(input)
      return template.render(context)
docs: Render a template from the template folder with the given context.
  
      Code based on
      `<https://github.com/mitsuhiko/flask/blob/master/flask/templating.py>`_
      :param input: the string template, or name of the template to be
                    rendered, or an iterable with template names
                    the first one existing will be rendered
      :param context: the variables that should be available in the
                      context of the template.
      :return: a string