defaulttags.py 文件源码

def render(self, context):
        from django.core.urlresolvers import reverse, NoReverseMatch
        args = [arg.resolve(context) for arg in self.args]
        kwargs = dict((smart_text(k, 'ascii'), v.resolve(context))
                      for k, v in self.kwargs.items())

        view_name = self.view_name.resolve(context)

        try:
            current_app = context.request.current_app
        except AttributeError:
            # Change the fallback value to None when the deprecation path for
            # Context.current_app completes in Django 2.0.
            current_app = context.current_app

        # Try to look up the URL twice: once given the view name, and again
        # relative to what we guess is the "main" app. If they both fail,
        # re-raise the NoReverseMatch unless we're using the
        # {% url ... as var %} construct in which case return nothing.
        url = ''
        try:
            url = reverse(view_name, args=args, kwargs=kwargs, current_app=current_app)
        except NoReverseMatch:
            exc_info = sys.exc_info()
            if settings.SETTINGS_MODULE:
                project_name = settings.SETTINGS_MODULE.split('.')[0]
                try:
                    url = reverse(project_name + '.' + view_name,
                              args=args, kwargs=kwargs,
                              current_app=current_app)
                except NoReverseMatch:
                    if self.asvar is None:
                        # Re-raise the original exception, not the one with
                        # the path relative to the project. This makes a
                        # better error message.
                        six.reraise(*exc_info)
            else:
                if self.asvar is None:
                    raise

        if self.asvar:
            context[self.asvar] = url
            return ''
        else:
            return url