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

Steven D'Aprano steve at pearwood.info
Wed May 28 02:07:59 CEST 2008

(If you receive this twice, please excuse the duplicate email. User-error on my part, sorry.)

On Wed, 28 May 2008 08:23:38 am Raymond Hettinger wrote:

A flatten() implementation doesn't really care about whether an input is a string which supports all the string-like methods such as capitalize().   Wouldn't it be better to write your version of flatten() with a registration function so that a user could specify which objects are atomic?  Otherwise, you will have to continually re-edit your flatten() code as you run across other non-stringlike objects that also need to be treated as atomic.

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.

Re-writing the above to match Python 3 is left as an exercise.

-- Steven

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