Using "with" context handler, and catching specific exception?

[Victor Hooi]

Hi,

I'm actually on Python 2.7, so we don't have access to any of those nice new exceptions in Python 3.3 =(:

http://docs.python.org/2.7/library/exceptions.html#exception-hierarchy

@Ben - Good point about just catching the more general exception, and just printing out the string message.

I suppose in most cases, we won't be doing anything special for the different types (e.g. file not found, permission error, is a directory etc.) - it'll just be going into logs.

Is there anything wrong with me just catching "Exception" in this case of opening a file, and printing the message from there?

Cheers,
Victor


On Tuesday, 22 October 2013 14:53:58 UTC+11, Ben Finney  wrote:
> Victor Hooi <victorhooi at gmail.com> writes:
> 
> 
> 
> > Aha, good point about IOError encapsulating other things, I'll use
> 
> > FileNotFoundError, and also add in some other except blocks for the
> 
> > other ones.
> 
> 
> 
> Or not; you can catch OSError, which is the parent of FileNotFoundError
> 
> <URL:http://docs.python.org/3/library/exceptions.html#exception-hierarchy>,
> 
> but don't assume in your code that it means anything more specific.
> 
> 
> 
> You should only catch specific exceptions if you're going to do
> 
> something specific with them. If all you want to do is log them and move
> 
> on, then catch a more general class and ask the exception object to
> 
> describe itself (by using it in a string context).
> 
> 
> 
> 
> 
> In versions of Python before 3.3, you have to catch EnvironmentError
> 
> <URL:http://docs.python.org/3.2/library/exceptions.html#EnvironmentError>
> 
> and then distinguish the specific errors by their ‘errno’ attribute
> 
> <URL:http://docs.python.org/3.2/library/errno.html>::
> 
> 
> 
>     import errno
> 
> 
> 
>     try:
> 
>         with open('somefile.log', 'wb') as f:
> 
>             f.write("hello there")
> 
>     except EnvironmentError as exc:
> 
>         if exc.errno == errno.ENOENT:
> 
>             handle_file_not_found_error()
> 
>         elif exc.errno == errno.EACCES:
> 
>             handle_permission_denied()
> 
>         elif exc.errno == errno.EEXIST:
> 
>             handle_file_exists()
> 
>         …
> 
>         else:
> 
>             handle_all_other_environment_errors()
> 
> 
> 
> That's much more clumsy, which is why it was improved in the latest
> 
> Python. If you can, code for Python 3.3 or higher.
> 
> 
> 
> -- 
> 
>  \     “Unix is an operating system, OS/2 is half an operating system, |
> 
>   `\    Windows is a shell, and DOS is a boot partition virus.” —Peter |
> 
> _o__)                                                        H. Coffin |
> 
> Ben Finney