[Python-Dev] Need a way to test for 8-bit-or-unicode-string

[Guido van Rossum]

> > - Create a common base class of str and unicode, which should be an
> >   abstract class.  This is the most OO solution, but I can't think of
> >   a good name; abstractstring is too long, AbstractString or String
> >   are uncommon naming conventions for built-in types, 'string' would
> >   almost work except that it's already the name of a very common
> >   module.[*]
> 
> +1. This would be nice and the same could be done for sequences, file-like
> objects and other common currently interface-defined object categories.
> 
> About the naming: how about numberclass, stringclass, sequenceclass, 
> fileclass ?!
> 
> Then you could write:
> 
> if isinstance(obj, stringclass): ...
> 
> which looks OK and is not too much typing.

Hm, I don't know if "class" is the proper suffix to mean "abstract
base class".  I think I'll either call it "numberbase" or
"abstractnumber".

> The advantage of this approach is that it can be extended to other
> types and classes as well (much like you can currently do with the
> Python exceptions).

Yup, that's why it's the most OO solution. :-)

> With the new type logic in place, how hard would it be making
> the existing built-in types subclasses of these base types ?

That would be a prerequisite!

> (also: is there a run-time penalty for this ?)

None.

> > - Make str a subclass of unicode (or vice versa).  This can't be done
> >   because subclassing requires implementation inheritance, in
> >   particular the instance structure layout must overlap.  Also, this
> >   would make it hard to check for either str or unicode.
> 
> -0. This would be hard to get right because the two objects use a 
> very different struct layout. Could be an option in the long run though.

I tried to explany that I already gave it a -1. ;-)

> > - Create a new service function, IsString(x) or isString(x) or
> >   isstring(x), that's a shortcut for "isinstance(x, str) or
> >   isinstance(x, unicode)".  The question them becomes where to put
> >   this: as a builtin, in types.py, or somewhere else...
> 
> -1. This mechanism can not be extended by e.g. UserStrings. 

Good point.

There's still Neil's isinstance(x, (str, unicode)) which gives the
programmer more freedom: maybe some function wants to support lists
and tuples but not all sequences.

I'm currently +1 on introducing names for abstract base classes *and*
extensing isinstance()'s API.

--Guido van Rossum (home page: http://www.python.org/~guido/)