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From: Peter Otten <__peter__@web.de>
Subject: Re: try... except with unknown error types
Date: Sat, 10 Sep 2011 12:17:23 +0200
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:13060

Chris Torek wrote:

> >>> import socket
> >>> isinstance(socket.error, IOError)
> False

Here you test if the socket.error *class* is an instance of IOError; this 
would print True if IOError were socket.error's metaclass. However:

>>> isinstance(socket.error(), IOError)
True

or more directly:

>>> issubclass(socket.error, IOError)
True
>>> issubclass(socket.error, EnvironmentError)
True

This is a relatively recent change:

$ python2.5 -c'from socket import error; print issubclass(error, IOError), 
issubclass(error, EnvironmentError)'
False False
$ python2.6 -c'from socket import error; print issubclass(error, IOError), 
issubclass(error, EnvironmentError)'
True True