cache.py 文件源码

def render(self, context):
        try:
            expire_time = self.expire_time_var.resolve(context)
        except VariableDoesNotExist:
            raise TemplateSyntaxError('"cache" tag got an unknown variable: %r' % self.expire_time_var.var)
        try:
            expire_time = int(expire_time)
        except (ValueError, TypeError):
            raise TemplateSyntaxError('"cache" tag got a non-integer timeout value: %r' % expire_time)
        if self.cache_name:
            try:
                cache_name = self.cache_name.resolve(context)
            except VariableDoesNotExist:
                raise TemplateSyntaxError('"cache" tag got an unknown variable: %r' % self.cache_name.var)
            try:
                fragment_cache = caches[cache_name]
            except InvalidCacheBackendError:
                raise TemplateSyntaxError('Invalid cache name specified for cache tag: %r' % cache_name)
        else:
            try:
                fragment_cache = caches['template_fragments']
            except InvalidCacheBackendError:
                fragment_cache = caches['default']

        vary_on = [var.resolve(context) for var in self.vary_on]
        cache_key = make_template_fragment_key(self.fragment_name, vary_on)
        value = fragment_cache.get(cache_key)
        if value is None:
            value = self.nodelist.render(context)
            fragment_cache.set(cache_key, value, expire_time)
        return value