«

Michael Foord came up with a much simpler
illustration. With Python 2.6::

>>> try:
... open('flooble')
... except Exception as e:
... pass
...
>>> e
IOError(2, 'No such file or directory')
>>> unicode(e)
u"(2, 'No such file or directory')"
>>> str(e)
"[Errno 2] No such file or directory: 'flooble'"
>>> u'%s' % e
u"(2, 'No such file or directory')"
>>> '%s' % e
"[Errno 2] No such file or directory: 'flooble'"

Cheers,
Alan Isaac

On Fri, Sep 11, 2009 at 3:12 PM, Alan G Isaac <> wrote:
> Michael Foord came up with a much simpler
> illustration. Â*With Python 2.6::
>
> Â* Â* Â* Â*>>> try:
> Â* Â* Â* Â*... Â*open('flooble')
> Â* Â* Â* Â*... except Exception as e:
> Â* Â* Â* Â*... Â*pass
> Â* Â* Â* Â*...
> Â* Â* Â* Â*>>> e
> Â* Â* Â* Â*IOError(2, 'No such file or directory')
> Â* Â* Â* Â*>>> unicode(e)
> Â* Â* Â* Â*u"(2, 'No such file or directory')"
> Â* Â* Â* Â*>>> str(e)
> Â* Â* Â* Â*"[Errno 2] No such file or directory: 'flooble'"
> Â* Â* Â* Â*>>> u'%s' % e
> Â* Â* Â* Â*u"(2, 'No such file or directory')"
> Â* Â* Â* Â*>>> '%s' % e
> Â* Â* Â* Â*"[Errno 2] No such file or directory: 'flooble'"

Sounds like IOError or one of its ancestors defines both __str__() and
__unicode__ () special methods but has them produce different output.

Cheers,
Chris
--
http://blog.rebertia.com

On Fri, 11 Sep 2009 15:19:05 -0700, Chris Rebert wrote:

> On Fri, Sep 11, 2009 at 3:12 PM, Alan G Isaac <>
> wrote:
>> Michael Foord came up with a much simpler illustration. Â*With Python
>> 2.6::

[snip]

> Sounds like IOError or one of its ancestors defines both __str__() and
> __unicode__ () special methods but has them produce different output.


That's what it looks like to me too, which I wouldn't call either a bug
or a feature. I don't think Python makes any promises regarding exception
messages.

However, I must admit I'm perplexed why the original example is calling
__unicode__() in the first place! Given the line:

raise self.severe('Problems with "%s" directive path:\n%s: %s.'
% (self.name, error.__class__.__name__, error))

it looks to me like it should be calling error.__str__() not
error.__unicode(). Making the suggested edit:

raise self.severe('Problems with "%s" directive path:\n%s: %s.'
% (self.name, error.__class__.__name__, str(error)))

should have no effect. But it (apparently) does. This brings us back to
Alan's original question:

"MYSTERY: how can "%s"%error be different from "%s"%str(error) in Python
2.6?"



--
Steven

2009/9/12 Steven D'Aprano <>:
> On Fri, 11 Sep 2009 15:19:05 -0700, Chris Rebert wrote:
>
>> Sounds like IOError or one of its ancestors defines both __str__() and
>> __unicode__ () special methods but has them produce different output.
>
>
> That's what it looks like to me too, which I wouldn't call either a bug
> or a feature. I don't think Python makes any promises regarding exception
> messages.
>
>

There are some report about the apparently same issue in the bug tracker.
http://bugs.python.org/issue5274
http://bugs.python.org/issue6108

vbr

On 9/11/2009 9:42 PM, Steven D'Aprano wrote:
> However, I must admit I'm perplexed why the original example is calling
> __unicode__() in the first place! Given the line:
>
> raise self.severe('Problems with "%s" directive path:\n%s: %s.'
> % (self.name, error.__class__.__name__, error))
>
> it looks to me like it should be calling error.__str__() not
> error.__unicode(). Making the suggested edit:
>
> raise self.severe('Problems with "%s" directive path:\n%s: %s.'
> % (self.name, error.__class__.__name__, str(error)))
>
> should have no effect. But it (apparently) does. This brings us back to
> Alan's original question:
>
> "MYSTERY: how can "%s"%error be different from "%s"%str(error) in Python
> 2.6?"


George Brandl explained it to me this way:

It's probably best explained with a bit of code:

>>> >>> class C(object):
... def __str__(self): return '[str]'
... def __unicode__(self): return '[unicode]'
...
>>> "%s %s" % ('foo', C())
'foo [str]'
>>> "%s %s" % (u'foo', C())
u'foo [unicode]'

I.e., as soon as a Unicode element is interpolated into a string, further
interpolations automatically request Unicode via __unicode__, if it exists.

Pretty subtle ...

Cheers,
Alan Isaac