[Python-ideas] PEP-3151 pattern-matching

[M.-A. Lemburg]

Antoine Pitrou wrote:
> On Fri, 08 Apr 2011 10:59:16 +0200
> "M.-A. Lemburg" <mal at egenix.com> wrote:
>>>
>>> I think EnvironmentError, WindowsError, VMSError, OSError, mmap.error
>>> and select.error should definitely all be merged with IOError, as they
>>> aren't used consistently enough to make handling them differently
>>> reliable even in current code.
>>
>> Their use may be inconsistent in a few places, but those cases
>> are still well-defined by the implementation, so code relying
>> on that well-defined behavior will break in subtle ways.
> 
> Another quirk occurred to me today: select.error doesn't derive from
> EnvironmentError, and so it doesn't have the errno attribute (even
> though the select module "correctly" instantiates it with a (errno,
> message) tuple). Also, its str() is borked:
> 
>>>> e = select.error(4, "interrupted")
>>>> str(e)
> "(4, 'interrupted')"
>>>> raise e
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> select.error: (4, 'interrupted')

Works fine in Python 2.7:

>>> import select
>>> e = select.error(4, "intr")
>>> e
error(4, 'intr')
>>> try:
...  raise e
... except select.error, x:
...  code, text = x
...  print code,text
...
4 intr
>>>

Note that existing code will not look for an attribute that
doesn't exist :-) It'll unwrap the tuple and work from there
or use the .args attribute to get at the constructor args.

-- 
Marc-Andre Lemburg
eGenix.com

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