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

Guido van Rossum guido@python.org
Fri, 05 Oct 2001 11:57:53 -0400

> - 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/)