Tornado中的`send_error`, `write_error`和`raise HTTPError`有什么区别?

Question

RT，官方文档看的不是很懂：RequestHandler.send_error(status_code=500,kwargs)**SendsthegivenHTTPerrorcodetothebrowser.Ifflush()hasalreadybeencalled,itisnotpossibletosendanerror,sothismethodwillsimplyterminatetheresponse.Ifoutputhasbeenwrittenbutnotyetflushed,itwillbediscardedandreplacedwiththeerrorpage.Overridewrite_error()tocustomizetheerrorpagethatisreturned.Additionalkeywordargumentsarepassedthroughtowrite_error.RequestHandler.write_error(status_code,kwargs)**Overridetoimplementcustomerrorpages.write_errormaycallwrite,render,set_header,etctoproduceoutputasusual.Ifthiserrorwascausedbyanuncaughtexception(includingHTTPError),anexc_infotriplewillbeavailableaskwargs["exc_info"].Notethatthisexceptionmaynotbethe“current”exceptionforpurposesofmethodslikesys.exc_info()ortraceback.format_exc.我理解的是send_error调用了write_error，所以写自定义错误页面的时候要自己实现write_error方法，抛出错误的时候使用send_error。那么又该在什么时候使用rasietornado.web.HTTPError呢？

Answer 1

HTTPError一般是用tornado访问某个url，然后这个url不存在，或者返回一个错误码的时候用到的。
fromtornado.httpclientimportHTTPClient,HTTPError
http_client=HTTPClient()
try:
response=http_client.fetch(url,method='GET',request_timeout=120)
exceptHTTPErrorashttp_error:
printhttp_error
exceptExceptionase:
printe
finally:
http_client.close()
                            

Answer 2

send_error是Torando发送错误状态码到浏览器,而write_error是对自定义的错误页面进行重写,是2个不同的操作。