[Python-Dev] Revised PEP 349: Allow str() to return unicode strings

Tue Aug 23 19:00:06 CEST 2005

On Tue, Aug 23, 2005 at 05:45:27PM +0200, Wolfgang Lipp wrote:
> i have to revise my last posting -- exporting the new ``str``
> pure-python implementation breaks -- of course! -- as soon
> as ``isinstance(x,str)`` [sic] is used

Right. I tried to come up with a pure Python version so people
could test their code. This was my latest attempt before giving
up (from memory):
 # inside site.py
 _old_str_new = str.__new__
 def _str_new(self, s):
 if type(self) not in (str, unicode):
 return _old_str_new(self, s)
 if type(s) not in (str, unicode):
 return s
 r = s.__str__()
 if not isinstance(r, (str, unicode)):
 raise TypeError('__str__ returned non-string')
 return r
 str.__new__ = _str_new

It doesn't work though:
 TypeError: can't set attributes of built-in/extension type 'str'
Maybe someone else has a clever solution.
 Neil