Handling exceptions with Py2 and Py3

[Pavlos Parissis]

On 27/05/2016 02:51 μμ, Steven D'Aprano wrote:
> On Fri, 27 May 2016 10:24 pm, Pavlos Parissis wrote:
> 
>> Hi,
>>
>> So, we have ConnectionRefusedError in Python3 but not in Python2.
>> Six module doesn't provide a wrapper about this.
>>
>> What is most efficient way to handle this situation in a try-catch block?
> 
> Um, could you give us a hint as to context?
> 

The following is inside a while true loop which implements a
retry logic.

try:

    unix_socket = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
    unix_socket.settimeout(0.5)
    unix_socket.connect(self.socket_file)
    unix_socket.send(six.b(command + '\n'))
    file_handle = unix_socket.makefile()
    data = file_handle.read().splitlines()
except ConnectionRefusedError:
    raised = SocketConnectionError(self.socket_file)
except socket.timeout:
    raised = SocketTimeout(socket_file=self.socket_file)
except OSError as error:

    if error.errno == 106:
        raised = SocketTransportError(socket_file=self.socket_file)
    else:
        raised = error
else:
    procecess(data)
finally:
    unix_socket.close()
    if raised:
        time.sleep(self.retry_interval)


> What does Python 2 raise instead of ConnectionRefusedError? I don't know, so
> for the sake of calling it *something* I'll say it's FooError. Then if it
> is a simple name, you can do this:
> 
> 
> if sys.version < "3":
>     ConnectionRefusedError = FooError
> 
> # much later
> try:
>    do_the_thing()
> except ConnectionRefusedError:
>     ...
> 
> 
> 
> Or instead of checking for the version, you can check for the name:
> 
> 
> try:
>     from some_module import ConnectionRefusedError
> except ImportError:
>     # Must be Python 2
>     from another_module import FooError as ConnectionRefusedError
> 
> 
> If neither of these techniques help, please give more context and we can be
> more specific.
> 
> 
> 

I will try the approach mentioned by Ben Finney as I am already checking 'errno'.

Thanks everyone for the replies.

Cheers,
Pavlos

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