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Unicode strings as arguments to exceptions

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  Unicode strings as arguments to exceptions Ernest Adrogué <nfdisco@gmail.com> - 2014-01-16 13:34 +0100
    Re: Unicode strings as arguments to exceptions Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-01-16 14:16 +0000
      Re: Unicode strings as arguments to exceptions Roy Smith <roy@panix.com> - 2014-01-16 09:32 -0500
      Re: Unicode strings as arguments to exceptions Terry Reedy <tjreedy@udel.edu> - 2014-01-16 18:48 -0500

#64077 — Unicode strings as arguments to exceptions

Hi,

There seems to be some inconsistency in the way exceptions handle Unicode
strings.  For instance, KeyError seems to not have a problem with them

>>> raise KeyError('a')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'a'
>>> raise KeyError(u'ä')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: u'\xe4'

On the other hand ValueError doesn't print anything.

>>> raise ValueError('a')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: a
>>> raise ValueError(u'ä')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError

I'm using Python 2.7.6 on a Unix machine.

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#64081

On Thu, 16 Jan 2014 13:34:08 +0100, Ernest Adrogué wrote:

> Hi,
> 
> There seems to be some inconsistency in the way exceptions handle
> Unicode strings.

Yes. I believe the problem lies in the __str__ method. For example, 
KeyError manages to handle Unicode, although in an ugly way:

py> str(KeyError(u'ä'))
"u'\\xe4'"

Hence:

py> raise KeyError(u'ä')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: u'\xe4'


While ValueError assumes ASCII and fails:

py> str(ValueError(u'ä'))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode character u'\xe4' in 
position 0: ordinal not in range(128)

When displaying the traceback, the error is suppressed, hence:

py> raise ValueError(u'ä')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError


I believe this might be accepted as a bug report on ValueError.


-- 
Steven

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#64083

In article <52d7e9a0$0$29999$c3e8da3$5496439d@news.astraweb.com>,
 Steven D'Aprano <steve+comp.lang.python@pearwood.info> wrote:

> On Thu, 16 Jan 2014 13:34:08 +0100, Ernest Adrogué wrote:
> 
> > Hi,
> > 
> > There seems to be some inconsistency in the way exceptions handle
> > Unicode strings.
> 
> Yes. I believe the problem lies in the __str__ method. For example, 
> KeyError manages to handle Unicode, although in an ugly way:
> 
> py> str(KeyError(u'ä'))
> "u'\\xe4'"
> 
> Hence:
> 
> py> raise KeyError(u'ä')
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> KeyError: u'\xe4'
> 
> 
> While ValueError assumes ASCII and fails:
> 
> py> str(ValueError(u'ä'))
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> UnicodeEncodeError: 'ascii' codec can't encode character u'\xe4' in 
> position 0: ordinal not in range(128)
> 
> When displaying the traceback, the error is suppressed, hence:
> 
> py> raise ValueError(u'ä')
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> ValueError
> 
> 
> I believe this might be accepted as a bug report on ValueError.

If you try to construct an instance of ValueError with an argument it 
can't handle, the obvious thing for it to do is raise ValueError :-)

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#64115

On 1/16/2014 9:16 AM, Steven D'Aprano wrote:
> On Thu, 16 Jan 2014 13:34:08 +0100, Ernest Adrogué wrote:
>
>> Hi,
>>
>> There seems to be some inconsistency in the way exceptions handle
>> Unicode strings.
>
> Yes. I believe the problem lies in the __str__ method. For example,
> KeyError manages to handle Unicode, although in an ugly way:
>
> py> str(KeyError(u'ä'))
> "u'\\xe4'"
>
> Hence:
>
> py> raise KeyError(u'ä')
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
> KeyError: u'\xe4'
>
>
> While ValueError assumes ASCII and fails:
>
> py> str(ValueError(u'ä'))
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
> UnicodeEncodeError: 'ascii' codec can't encode character u'\xe4' in
> position 0: ordinal not in range(128)
>
> When displaying the traceback, the error is suppressed, hence:
>
> py> raise ValueError(u'ä')
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
> ValueError
>
> I believe this might be accepted as a bug report on ValueError.

Or a change might be rejected as a feature change or as a bugfix that 
might break existing code. We do change exception messages in new 
versions but do not normally do so in bugfix releases.

http://bugs.python.org/issue1012952 is related but different. The issue 
there was that unicode(ValueError(u'ä')) gave the same 
UnicodeEncodeError as str(ValueError(u'ä')). That was fixed by giving 
exceptions a __unicode__ method, but that did not fix the traceback 
display issue above.

http://bugs.python.org/issue6108
unicode(exception) and str(exception) should return the same message
also seems related. The issue was raised what str should do if the 
unicode message had non-ascii chars. I did not read enough to find an 
answer. The same question would arise here.

-- 
Terry Jan Reedy

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