[Python-Dev] __str__ vs. __unicode__

[M.-A. Lemburg]

Walter Dörwald wrote:
> __str__ and __unicode__ seem to behave differently. A __str__
> overwrite in a str subclass is used when calling str(), a __unicode__
> overwrite in a unicode subclass is *not* used when calling unicode():
> 
> -------------------------------
> class str2(str):
>     def __str__(self):
>         return "foo"
> 
> x = str2("bar")
> print str(x)
> 
> class unicode2(unicode):
>     def __unicode__(self):
>         return u"foo"
> 
> x = unicode2(u"bar")
> print unicode(x)
> -------------------------------
> 
> This outputs:
> foo
> bar
> 
> IMHO this should be fixed so that __unicode__() is used in the
> second case too.

If you drop the base class for unicode, this already works.

This code in object.c:PyObject_Unicode() is responsible for
the sub-class version not doing what you'd expect:

	if (PyUnicode_Check(v)) {
		/* For a Unicode subtype that's not a Unicode object,
		   return a true Unicode object with the same data. */
		return PyUnicode_FromUnicode(PyUnicode_AS_UNICODE(v),
					     PyUnicode_GET_SIZE(v));
	}

So the question is whether conversion of a Unicode sub-type
to a true Unicode object should honor __unicode__ or not.

The same question can be asked for many other types, e.g.
floats (and __float__), integers (and __int__), etc.

 >>> class float2(float):
...     def __float__(self):
...             return 3.141
...
 >>> float(float2(1.23))
1.23
 >>> class int2(int):
...     def __int__(self):
...             return 42
...
 >>> int(int2(123))
123

I think we need general consensus on what the strategy
should be: honor these special hooks in conversions
to base types or not ?

Maybe the string case is the real problem ... :-)

-- 
Marc-Andre Lemburg
eGenix.com

Professional Python Services directly from the Source  (#1, Jan 10 2005)
 >>> Python/Zope Consulting and Support ...        http://www.egenix.com/
 >>> mxODBC.Zope.Database.Adapter ...             http://zope.egenix.com/
 >>> mxODBC, mxDateTime, mxTextTools ...        http://python.egenix.com/
________________________________________________________________________

::: Try mxODBC.Zope.DA for Windows,Linux,Solaris,FreeBSD for free ! ::::