[Python-Dev] Iterable String Redux (aka String ABC)

[Armin Ronacher]

Hi,

Strings are currently iterable and it was stated multiple times that this is a
good idea and shouldn't change.  While I still don't think that that's a good
idea I would like to propose a solution for the problem many people are
experiencing by introducing an abstract base class for strings.

Basically *the* problematic situation with iterable strings is something like
a `flatten` function that flattens out every iterable object except of strings.
Imagine it's implemented in a way similar to that::

    def flatten(iterable):
        for item in iterable:
            try:
                if isinstance(item, basestring):
                    raise TypeError()
                iterator = iter(item)
            except TypeError:
                yield item
            else:
                for i in flatten(iterator):
                    yield i

A problem comes up as soon as user defined strings (such as UserString) is
passed to the function.  In my opinion a good solution would be a "String"
ABC one could test against.


Regards,
Armin