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

Terry Reedy tjreedy at udel.edu
Wed May 28 00:58:14 CEST 2008

"Armin Ronacher" <armin.ronacher at active-4.com> wrote in message news:loom.20080527T192243-415 at post.gmane.org... | Basically the problematic situation with iterable strings is something like | a flatten function that flattens out every iterable object except of strings.

In most real cases I can imagine, this is way too broad. For instance, trying to 'flatten' an infinite iterable makes the flatten output one also. Flattening a set imposes an arbitrary order (but that is ok if one feeds the output to set(), which de-orders it). Flattening a dict decouples keys and values. Flattening iterable set-theoretic numbers (0={}, n = {n-1, {n-1}}, or something like that) would literaly yield nothing.

| 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

I can more easily imagine wanting to flatten only certain classes, such and tuples and lists, or frozensets and sets.

def flatten(iterable, classes): for item in iterable: if type(item) in classes: for i in flatten(item, classes): yield i else: yield item

| 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.

This might be a good idea regardless of my comments.

tjr

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