[Tutor] use of __new__

[spir]

On Fri, 12 Mar 2010 12:27:02 +1100
Steven D'Aprano <steve at pearwood.info> wrote:

> On Fri, 12 Mar 2010 11:53:16 am Steven D'Aprano wrote:
> 
> > I have tried to match the behaviour of the built-in unicode as close
> > as I am able. See here:
> > http://docs.python.org/library/functions.html#unicode
> 
> And by doing so, I entirely forgot that you want to change the default 
> encoding from 'ascii' to 'utf-8'! Oops. Sorry about that.
> 
> Try changing this bit:
> 
> >         else:  # Never attempt decoding.
> >             obj = super(Unicode, cls).__new__(Unicode, string)

I get it! The call to new must pass the target class as argument:

    obj = unicode.__new__(Unicode, string, encoding)
                          ^
while I passed unicode instead. I guess this is the bit that decides on the final class of the return obj.

> to this:
> 
>         # Untested
>         else:
>             if isinstance(string, unicode):
>                 # Don't do any decoding.
>                 obj = super(Unicode, cls).__new__(Unicode, string)
>             else:
>                 if encoding is None: encoding = cls._ENCODING
>                 if errors is None: errors = cls._ERRORS
>                 obj = super(Unicode, cls).__new__(
>                   Unicode, string, encoding, errors)

Thank you again, Steven.

Denis
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