[ python-Bugs-1706815 ] socket.error exceptions not subclass of StandardError

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Bugs item #1706815, was opened at 2007-04-24 11:09
Message generated for change (Comment added) made by greg
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Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: John Nagle (nagle)
>Assigned to: Gregory P. Smith (greg)
Summary: socket.error exceptions not subclass of StandardError

Initial Comment:
The "socket.error" exception is a subclass of Exception, but not of StandardError.  It needs to be placed properly in the exception hierarchy, presumably somewhere under IOError.

Socket errors have some known problems.  See also:

[ 805194 ] Inappropriate error received using socket timeout
[ 1019808 ] wrong socket error returned
[ 1571878 ] Improvements to socket module exceptions
[ 708927 ] socket timeouts produce wrong errors in win32 

Just figuring out what exceptions can be raised from the socket module is tough.  I've seen exceptions derived from "socket.error", exceptions from IOError, and exceptions from the SSL layer, which patches the
sockets module when loaded.  These are non-bug exceptions; that is, the problem is out in the network, external to the program.

Some are retryable, some indicate that a different approach (different port, different protocol) should be tried, and some mean that some named resource doesn't exist.  Programs need to make those distinctions reliably.

The most important distinction with sockets is "external network problem" vs. "local program program".  To resolve this, I suggest a "NetworkException" in the exception hierarchy, with all the things that can go wrong due to conditions external to the local machine under that exception.

I'd suggest the following:

1.  Add "NetworkError" under "IOError" in the exception hierarchy.

2.  Put the existing "socket.error" under "NetworkError". Since "socket.error" needs to be reparented anyway (it's currently a direct descendant of "Exception") this provides a good place for it.

3.  Find any places where the socket module can raise IOError or OSError due to an external network condition, and make them raise something under NetworkError instead.  Code that catches IOError will still work.

4.  Put all errors in the various SSL modules (SSLError, etc.) which can be raised due to external network conditions under "NetworkError"

5.  Move "urllib2.URLError", which is currently under IOError, down a level under NetworkError.

6.  Move the misc. errors from "urllib", like "ContentTooShortError", which are currently under IOError, down a level under NetworkError.

7.  URL translation errors from the IDNA (Unicode URL encoding) module probably should raise an error similar to that for an incorrect URL, rather than raising a UnicodeError.  

Then, programs that catch NetworkError could be sure of catching all network trouble conditions, but not local code bugs. 

With these changes, any exception that's being caught now will still be caught.

I'd suggest doing 1) above immediately, since that's a clear bug, but the others need to be discussed.

             

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>Comment By: Gregory P. Smith (greg)
Date: 2007-07-02 16:39

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agreed! the above suggestions sound good.

for number (3) if there are any places that raise OSError, that could lead
to code upgrade headaches as the new NetworkError would not be a subclass
of OSError.  imho thats fine but others may disagree.

i am looking at implementing the immediate (1) and (2) as a starting
point.

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Comment By: John Nagle (nagle)
Date: 2007-04-24 11:12

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(See also PEP 352).

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