[Python-Dev] unicode and str (original) (raw)

Neil Schemenauer nas at arctrix.com
Mon Aug 30 22🔞16 CEST 2004

With Python 2.4:

>>> u = u'\N{WHITE SMILING FACE}'
>>> class A:
...   def __str__(self):
...     return u
... 
>>> class B:
...   def __unicode__(self):
...     return u
... 
>>> u'%s' % A()
u'\u263a'
>>> u'%s' % B()
u'\u263a'

With Python 2.3:

>>> u'%s' % A()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
UnicodeEncodeError: 'ascii' codec can't encode character u'\u263a' in
    position 0: ordinal not in range(128)
>>> u'%s' % B()
u'<__main__.B instance at 0x401f910c>'

The only thing I found in the NEWS file that seemed relevant is this note:

u'%s' % obj will now try obj.unicode() first and fallback to obj.str() if no unicode method can be found.

I don't think that describes the behavior difference. Allowing str return unicode strings seems like a pretty noteworthy change (assuming that's what actually happened).

Also, I'm a little unclear on the purpose of the unicode method. If you can return unicode from str then why would I want to provide a unicode method? Perhaps it is meant for objects that can either return a unicode or a string representation depending on what the caller prefers. I have a hard time imagining a use for that.

Neil

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