AppEngine / Python：为什么不抓住异常？

Question

我正在尝试编写一个Google-Appengine应用程序，当数据存储区写入被禁用时，该应用程序将很好地失败

目前我的main（）看起来像这样：

def main():
    make_datastore_readonly()
    try:
        run_wsgi_app(application)
    except CapabilityDisabledError:
        run_wsgi_app(NoWrite)

---

如果我将main设置为：

 def main(): run_wsgi_app(application) 

我的应用程序在引发异常时显示回溯。

---

如果我将main设置为：

 def main(): run_wsgi_app(NoWrite) 

它将正确显示我的错误消息（尽管对于每个请求）。

---

回到我修改过的main版本，这个版本：

def make_datastore_readonly():
  """Throw ReadOnlyError on put and delete operations."""
  def hook(service, call, request, response):
    assert(service == 'datastore_v3')
    if call in ('Put', 'Delete'):
      raise CapabilityDisabledError('Datastore is in read-only mode') //Line 18
  apiproxy_stub_map.apiproxy.GetPreCallHooks().Push('readonly_datastore', hook, 'datastore_v3')

我得到的回溯看起来像这样，而不是收到我的错误信息：

 Traceback (most recent call last): File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/webapp/_webapp25.py", line 703, in __call__ handler.post(*groups) File "/Users/kevin/Sche/main.py", line 232, in post me.put(); File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/db/__init__.py", line 1074, in put return datastore.Put(self._entity, **kwargs) File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/api/datastore.py", line 579, in Put return PutAsync(entities, **kwargs).get_result() File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/api/datastore.py", line 556, in PutAsync return _GetConnection().async_put(config, entities, local_extra_hook) File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/datastore/datastore_rpc.py", line 1553, in async_put return make_put_call(base_req, pbs, extra_hook) File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/datastore/datastore_rpc.py", line 1543, in make_put_call self.__put_hook, user_data) File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/datastore/datastore_rpc.py", line 1188, in make_rpc_call rpc.make_call(method, request, response, get_result_hook, user_data) File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/api/apiproxy_stub_map.py", line 519, in make_call self.__service, method, request, response, self.__rpc) File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/api/apiproxy_stub_map.py", line 207, in Call function(service, call, request, response) File "/Users/kevin/Sche/main.py", line 18, in hook raise CapabilityDisabledError('Datastore is in read-only mode') CapabilityDisabledError: Datastore is in read-only mode 

所以，我的问题是，为什么不抓住例外？

编辑：

此函数来自此StackOverflow答案

 def make_datastore_readonly(): """Throw ReadOnlyError on put and delete operations.""" def hook(service, call, request, response): assert(service == 'datastore_v3') if call in ('Put', 'Delete'): raise CapabilityDisabledError('Datastore is in read-only mode') //Line 18 apiproxy_stub_map.apiproxy.GetPreCallHooks().Push('readonly_datastore', hook, 'datastore_v3') 

Answer 1

main函数只注册此应用程序。 因此，在main函数中不会引发异常。 因此try ... catch语句将不起作用。

处理此异常的方法是定义新的RequestHandler。 然后，所有想要拥有此功能的请求都应该来自新的RequestHandler。

例如：

Class MyRequestHandler(RequestHandler):
    def get(self):
        try:
            self.get_handler()
        except CapabilityDisabledError:
            pass

class MyRequest(MyRequestHandler):
    def get_handler(self):
        # ....
        pass