[Python-Dev] __str__ vs. __unicode__

[M.-A. Lemburg]

Nick Coghlan wrote:
> M.-A. Lemburg wrote:
> 
>>> So if we fix __str__ this would be a bugfix for 2.4.1.
>>> If we fix the rest, this would be a new feature for 2.5.
>>
>>
>>
>> I have a feeling that we're better off with the bug fix than
>> the new feature.
>>
>> __str__ and __unicode__ as well as the other hooks were
>> specifically added for the type constructors to use.
>> However, these were added at a time where sub-classing
>> of types was not possible, so it's time now to reconsider
>> whether this functionality should be extended to sub-classes
>> as well.
> 
> 
> It seems oddly inconsistent though:
> 
> """Define __str__ to determine what your class returns for str(x).
> 
> NOTE: This won't work if your class directly or indirectly inherits from 
> str. If that is the case, you cannot alter the results of str(x)."""
> 
> At present, most of the type constructors need the caveat, whereas 
> __str__ actually agrees with the simple explanation in the first line.
> 
> Going back to PyUnicode, PyObject_Unicode's handling of subclasses of 
> builtins is decidedly odd:

Those APIs were all written long before there were sub-classes
of types.

> Py> class C(str):
> ...   def __str__(self): return "I am a string!"
> ...   def __unicode__(self): return "I am not unicode!"
> ...
> Py> c = C()
> Py> str(c)
> 'I am a string!'
> Py> unicode(c)
> u''

Ah, looks as if the function needs a general overhaul :-)

This section should be do a PyString_CheckExact():

	if (PyString_Check(v)) {
		Py_INCREF(v);
	    	res = v;
     	}

But before we start hacking the function, we need a general
picture of what we think is right.

Note, BTW, that there is also a tp_str slot that serves
as hook. The overall solution to this apparent mess should
be consistent for all hooks (__str__, tp_str, __unicode__
and a future tp_unicode).

-- 
Marc-Andre Lemburg
eGenix.com

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