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

[Terry Reedy]

"Steven D'Aprano" <steve at pearwood.info> wrote in message 
news:200805281007.59902.steve at pearwood.info...

Just throwing a suggestion out there...

def atomic(obj, _atomic=(basestring,)):
    try:
        return bool(obj.__atomic__)
    except AttributeError:
        if isinstance(obj, _atomic):
            return True
        else:
            try:
                iter(obj)
            except TypeError:
                return True
    return False

assert atomic("abc")
assert not atomic(['a', 'b', 'c'])

If built-in objects grew an __atomic__ attribute, you could simplify the
atomic() function greatly:

def atomic(obj):
    return bool(obj.__atomic__)


However atomic() is defined, now flatten() is easy:

def flatten(obj):
    if atomic(obj):
        yield obj
    else:
        for item in obj:
            for i in flatten(item):
                yield i


If you needed more control, you could customise it using standard
techniques e.g. shadow the atomic() function with your own version,
sub-class the types you wish to treat differently, make __atomic__ a
computed property instead of a simple attribute, etc.
==================

This is a lot of work to avoid being explicit about either atomic or 
non-atomic classes on an site, package, module, or call basis ;-)