code: def _exec_template(callable_, context, args=None, kwargs=None):
      
      template = context._with_template
      if template is not None and \
              (template.format_exceptions or template.error_handler):
          try:
              callable_(context, *args, **kwargs)
          except Exception:
              _render_error(template, context, compat.exception_as())
          except:
              e = sys.exc_info()[0]
              _render_error(template, context, e)
      else:
          callable_(context, *args, **kwargs)
docs: execute a rendering callable given the callable, a
      Context, and optional explicit arguments
  
      the contextual Template will be located if it exists, and
      the error handling options specified on that Template will
      be interpreted here.