[Twisted-Python] Trapping exceptions in Deferred

[Louis D. Burr]

Hi Mashiat,

> On May 12, 2015, at 9:53 AM, Mashiat Sarker Shakkhar <mashiat.sarker at gmail.com> wrote:
> 
> Hi
> 
> If I want to trap a certain type of exception in a deferred call, how do I specify it? For example, I see a failure like this:
> 
>     [HTTP11ClientProtocol (TLSMemoryBIOProtocol),client] [<twisted.python.failure.Failure <class 'OpenSSL.SSL.Error'>>]
>     [HTTP11ClientProtocol (TLSMemoryBIOProtocol),client] Traceback (most recent call last):
>     [HTTP11ClientProtocol (TLSMemoryBIOProtocol),client] Failure: twisted.web._newclient.ResponseNeverReceived: [<twisted.python.
> failure.Failure <class 'OpenSSL.SSL.Error'>>]
> 
> I want to trap all such failures. I tried `failure.trap(twisted.web._newclient.ResponseNeverReceived)` but looks like that did not work. My deferred callback looks like this:
> 
>     from twisted.internet.error import TimeoutError
>     from twisted.web._newclient import ResponseNeverReceived
>     def log_ignore_network_errors(failure):
>         print failure.getErrorMessage()
>         failure.printTraceback()
>         failure.trap(TimeoutError, ResponseNeverReceived)
> 
> Apparently this does not catch all such errors. What am I doing wrong here?
> 
This code sample does not indicate that you have actually assigned log_ignore_network_errors as an errback on a Deferred anywhere.  If you can provide a working code example that demonstrates your issue, it will be easier to help you :)

L. Daniel Burr

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